annasea:
Well, since I leave for my course in 9 days, getting into shape is not an option.
...
I agree that anxiety is my main drawback.
9 days is plenty of time. Swimming is not something we do naturally, so you can improve a great deal just by getting your body used to the motions. Just get some swimming meters in. While you are swimming, work on staying streamlined, doing powerful pulls and maximizing the glide. You do not want to work on speed, doubling your speed in water requires an eightfold increase in power - the energy from that increase comes directly out of your oxygen supplies.
A couple tips on dealing with the anxiety while breathholding. First, do some breathholding while swimming on the surface. Since you can get air by just lifting your head, your body won't have any cause to panic. Second, do the push off and add a stroke at a time practice I mentioned in my last post.
Here's a sample workout that will probably take 30-45 minutes. I'm assuming you have a 25M (or yard) pool, if not adjust as necessary. I'd try to do this at least 3 or 4 times before you go, with more being better. If you find this is too hard, cut down the number of repetitions of each set.
warmup - 4 lengths easy without stopping
technique work
- swim 1 length, rest 30 seconds, repeat for 8 times total
- swim 2 lengths, rest 60 seconds, 4 sets
breath work - rest at least 60 seconds between each swim, breathe normally while resting
- on surface, concentrating on form push off and swim as far as you can without breathing, catch your breath and finish length, repeat 6 times
- underwater, concentrating on form push off and glide as far as you can, return to wall and repeat 5 times
- underwater, concentrating on form push off, glide, take one stroke and glide as far as you can, return to wall and repeat 5 times
- repeat adding strokes until you feel you are getting to your breathholding limit, the idea here is to work on your technique and comfort underwater, not to go for your distance record
distance attempt
- go for max distance using tips from previous posts, 2 or 3 tries with plenty of rest
warmdown - 4 lengths easy without stopping
If you haven't reached the 20M by then, on the last day before you leave, do the distance attempt right after the warmup so you are still fresh. I bet you won't have any trouble.