Hi Cloudchaser,
I think you are pretty normal...I do most of my flying multi engine these days, and around 1 or 2 thousand.
If I take a single engine to altitude, I start thinking about the little mast holding the head etc...which is pretty silly really, considering a fall from 50ft will do you in just the same as one from 5000...and in my earlier days, I used to fly singles at high altitude with no worries or cares...IMC too
These seem to be feelings that cut in over 40 years of age, from what other pilots have shared...
I just grit my teeth and look at the map....