Wow! I didn't expect to get so many helping messages in such a short time! I'm not too much into the internet, connecting once a day at the most, so I apologise for not answering before.
Even though I'd like to say something to each of you who have so kindly taken the time to help me, I'm afraid I'll have to send a general posting (which I suppose is good, seeing how much I write!). The exception is Julius SCHMIDT. I hope you weren't upset when I said I didn't know whether you were serious or not; you comment about the psychology thesis puzzled me. I thought it might be some kind of joke. Maybe because I have trouble with the nuances of English, or maybe because I didn't see myself as having any type of psychological problem. But, as I said, sometimes one is the last to know. I apologise for having doubted your intentions.
First of all, I'm from Spain. As I said, there's only this dive instructor in my area, though now that you've suggested so, I could try some others in Madrid, which is at a two-hour ride from here. My instructor represents ACUC. Each of the OWD courses consists of four sessions, approximately one hour and forty-five minutes each (that includes explanations, setting up the equipment and actually doing the exercises, though I cannot say how much time is devoted to each part). In both of the courses, there were eight students and two instructors.
After one year, I don't remember the sequence very well, but the first day is all done with the snorkel. First we dive from here to there to get used to the fins (sorry, I misused the term "swim" in my original post, and didn't realise it until I read TMHeimer's answer... I should have said "dive", but I keep on thinking of "swimming" as moving from one place of the swimming pool to another). On that day we also remove our masks so we can try breathing through the snorkel without them. On the second day we already use all the equipment (except for the wetsuit). As I remember it, this is the only day we do some kneeling: the instructor kneels in front of us, and each removes and empties his mask. Then he explains how to share the air source, checks each of us can do it, and then we spend the rest of the session doing the same as we dive, and diving without the mask. On the third day we learn how to put the BCD on in the water, we practice going here and there in couples or groups of four, and buoyancy in general. On the fourth day we practise diving with only one fin, without fins, and without fins plus an empty BCD with the low-pressure inflating hose disconnected, and putting the fins on underwater.
I could see the logic behind repeating the same course once and again, since even with the best of instructors, I'm aware that I do need more time to do what others do, and since the swimming pool time allotted to the dive center is what it is, there's no way to get more time than doing another course (I already enquired). Anyway, the instructor was kind enough to let me do the second course for free. I've paid for the third one without asking anything, because I understand I'm using up his time and taking the place another student could be using. The private covered swimming pool is used only for organised sports (the dive centre, a water polo team, a competition swimming club), not open to individuals. The open-air swimming pool at my place opens only from June to September, but no snorkels or masks are allowed (only goggles), so I practise in the washbasin at home. This helps with the no-mask issue, but certainly not with the rest.
Some of you have suggested trying a different instructor. In principle, it sounds like a logical thing to do. But my present instructor told us at the beginning of the course that he was the type who doesn't give a certification away just because you've paid for the course, though many others do. I think that I'd be afraid to be one of those undeserving divers if I happen to pass the exams with my new instructor. As a matter of fact, I felt relieved when I heard my instructor say so, because I thought that if I ever get the OWD certification, it'll be because I am really fit for it, not because he wants to have a new customer buying equipment and other courses from him.
What I find sort of amusing is that so many people have suggested some sort of psychological help. I don't consider myself pesimistic or having low self-esteem, but just realistic. In fact, I remember feeling frustrated at not being able to be as good as others at sports before it dawned on me that I just couldn't do it, in the same way others couldn't draw or sing in tune, and that I wasn't worse than others as a human being because of it. It's true that this attitude may make me miss things only because I won't even try. But when I decide to try them (like in the case of diving), it's because I'd like to do them, so if I succeed, I'm delighted, and if I fail, I'm happy to have tried. For example, swimming (someone asked about it) is one of those things I managed to learn, after three courses, though -as I said in my first message- not at a very good level. Until I was a teenager I used to play in the swimming pool with my friends and cousins, but the most difficult thing I've done as far as diving is concerned is going to the deep (3 metres) end of the pool and descending and ascending quickly in a vertical position for several times in a row -something I don't think is quite wise after learning the OWD theory-, and diving under someone's legs without goggles, mask or snorkel (which proves I can be underwater, and that the problem arises when I want to do that and breathe at the same time). Anyway, before my first OWD course I mentioned this in the dive centre, and they told me that what I could do, swimming-wise, was enough, and that I might even improve my swimming skills by applying things learnt in the OWD course.
The panicking problem is something different. I have no idea how I'd react in such a situation, because it hasn't happened so far. It's true: probably I wouldn't react in the right way, but I'm not sure. The closest I've been to that is when I removed my mask underwater, and at no point did I feel the urge to go to the surface... Which is something, though not much.
The idea of thinking of all the steps I must take carefully and slowly before doing something souds great. In fact, my only qualm about the courses I've made is how rushed everything seems. Before we jump into the swimming pool, we're in a big hurry, because there's not much time and we cannot waste it. I acknowledge I'm in a slightly nervous attitude until I'm in the water, and even when I'm with the snorkel listening to instructions. But once I get underwater, everything seems so calm that I feel completely relaxed (except when I'm neither wearing a mask nor holding my nose with my fingers).
Thanks a lot, once again, for your valuable advice. I've printed all of your messages so as to go through them carefully again. I appreciate being told sincerely that diving is not for everyone. It'll really make me feel better if I don't succeed. I'd also like to thank those who have pointed out that my problems are not uncommon, though I may have been the unlucky one to combine them all. All of this will make the conversation I inted to have with my instructor at the end of the forthcoming course much more productive.
Now that I've tried it, I'm more willing than ever to put in all the effort which is required. I do love the feeling of being underwater, and I understand the importance of learning all the safety procedures well so that diving will be pleasurable and not dangerous. This is what I said before: even if I have to give up, I'm extremely happy to have tried. Even though every single day of my OWD courses has been part success and part failure, there's not one when I haven't got out of the swimming pool with a smile on my face. Wish me luck!