Lief,
I dont know of any experienced climber who doesn't get a little nervy once in a while.Dan put it well.Your gear you can trust, it's the tree that might be the X factor and that alone might pucker your butt tighter then a bulls ass during fly time.Any experienced climber who says they never get scared , or a little jittery is full of it.They just dont addmit it and dont show the sighns a newbe would.I've done recreational climbs that would make any experienced climber quiver.JUST CLIMBING IS NOT ALWAYS A WALK IN THE PARK.
One thing that might help you and something I teach new climbers when a little skittish in a tree; is to just concentrate on where your at and where you need to go. Dot let your mind wounder and think about how high you are. Keep your eyes leval and on the task at hand.Dont try and take in the whole relm of the tree, but instead take it a bite at a time, or I should say limb at a time.
Second thing that might help, is just plain committ.If you have to go out on a limb and have doubts, then you will be doubtful all they way if you make it.If you committ to going out on the limb with a plan of attack, then you'll probably make without a problem. This will then boost your confindence for the next go around and you'll come out of the tree with a smile, instead of having to clean your drawers.
Thanks
Greg