It sounds like you were overmedicated, and therefore hyper, on 100 mcg.
Dosage is somewhat weight-based, and your weight loss might have made it just a bit
too much for you.
I understand your concerns about going back to 100 mcg, and I wouldn't want to, either. There are alternatives. Jumping from 100 to 50 is most likely going to make you hypo before too long. That's too big a jump.