I had a painful fall last December while on a laid back group ride- I was drafting my training partner then let myself get distracted & started to half-wheel him. Seconds later, when he made a sideways movement, BAM! Down I went...
I thought I was fine except for some road rash. I went on training all winter- usually solitary or leading my local shop's "B" ride on the weekends. A few weeks ago, I go for my first "big" group ride since the wreck... all of a sudden, I find that I'm annoying other riders by letting a gap form between me & the person in front of me or by riding off to the side of the wheel in front of me. I try to correct myself but find that when I do, I get very nervous & tense and start grabbing my brakes at the slightest change in pace (an even bigger paceline sin!)
Being a racer, this is tough. I'm basically re-learning how to draft! My strategy is to start easy and very controlled. I go out with my training partner on a flat, smooth road. He pegs his speed at exactly 19mph. I get behind him and draft in "intervals"- I'll get very close for 1-2 minutes then back off a little for a mental break. We're now adding in turns & hills. We're also going to take our bikes out into the field behind my house & practice rubbing wheels on purpose. My first crit is in less than a month

My point- just like everyone else said- when you're ready, take baby steps, but work your way up to facing what you're ultimately scared of!