Some of us need gentler introductions than others. I was lucky that I did my certification dives in the absolutely calm and still water of the Coves at Alki, in Puget Sound. The only stressful condition I had to cope with was very poor visibility.
At about 40 dives, I went to Australia and had to jump into very choppy surface water for the first time. It was anxiety-producing for a few minutes, until I realized I was fine with a regulator in my mouth. But by that time, I was happy being in the water and comfortable in my gear. I could cope with one stressor.
A year later, I had to do some challenging exits in heavy swell onto a boat ladder. Again, it was anxiety-producing, but again, I was comfortable with everything ELSE that was going on.
You got a nasty first experience, which raised your anxiety level for the next time. What you needed was a very benign entry and an uneventful dive, and what you got was choppy surface conditions and current. I'm not sure I would have been brave enough as an instructor to make the decision Brad made, which was that if he could get you underwater, you would relax, but he did it and it worked.
Everybody IS making a good point that you need some strength and stamina to do this, because choppy water and current are the rule rather than the exception in many places, and being physically stressed to cope with the needs of the dive is not a good place to start. And, if you tend toward some nervousness, especially in the beginning, try to minimize the stressors in any given dive. Don't gang up on yourself.
You sound like me. You may be a person who needs to do a lot of simple diving and build confidence and relaxation, and then start adding the challenging stuff. You just have to be aware that, if you're not confident, you shouldn't be anyplace very deep or with much potential to get into trouble.
I agree with some of the people though, I would advise you to improve your cardiovascular/ muscular endurance to become a safer(and happier!) diver. 
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