Rear Suspension Setup So the situation is, about six months ago I got myself my first full sus trail bike Trek Fuel ex7.  For the most part, loving it.
Over that time I've had a number of spills, the most recent resulting in a trip to A&amp;E.
I might be grasping at straws here a little, but most of these spills have followed the same pattern.  Basically, when the rear shock is under heavy compression for say going off a drop off my bike kind of squirts forward out from under me.

While I'm sure this is probably largely caused by my own poor technique, I'm beginning to wonder if I don't quite have my suspension dialed in quite right.  I'm pretty happy with the say I've got, seems around 20ish% but I have no idea about the rebound settings.  I've used the recommendations from Trek but really don't have any idea if it's right for me.

So, is this a rider problem, or could/would incorrect setup be contributing?
Likely a a better rider would have stayed on, and there is work to do on you technique, but your suspension should not miss behaving like that. Your comment about rebound settings strongly suggests to me that will the route cause of the problem. 

Sag is at the very best a starting point. Once you have the sag correct, you have a 'stake in the ground' to start tuning the suspension. The other settings are perfect for the average rider. The average rider has 2.5 kids, 13 feet a white picket fence and 1.2 dogs, my guess is you are not average :).

Have a look at this video. MTB Suspension Setup - How To Get It Dialed In 10-Minutes

The sag sets the amount of support the suspension offers - too little and you bottom out, too much and you don't get to use all the travel and don't get the benefit of it. Rebound sets the rate the suspension comes back after being compressed. Too fast rebound and you experience what you have had happen - the bike 'bounces' and you loose control (on the front the wheel lifts and it gets sketchy, on the back, you get flicked up, which with weight back and too straight legs could be turned into forward surge ). Too slow rebound and the shock /fork has not recovered before the next bump. After a few bumps, you have run out of travel. 

The idea is get the rebound of the front and back balanced so the whole bike lifts evenly. You also need to get it so it rebounds just fast enough to recover, without being so fast it lifts wheels off the ground. 

If anything, set rebound slower than ideal, and speed it up until you feel its too fast, then wind it back a notch or two.