I really feel this. I'm supposed to be half coding and half support but the support has expanded to fill all my time and I don't write anything more than 30-line kludges that only I will see any more.
That's partly just the nature of support always taking up all the time, but also I feel really paralysed when it comes to coding, because I just think of all the stupid corner cases I've been bitten by and how bad it felt to lose data or cause downtime or just look stupid.
And yes, the answer might be "write more test cases, code review" but that little voice in the back of my head goes "you thought you'd caught all the edge cases last time, and it still did a dumb thing you'd never thought of". I find it really demotivating, and start to put things off until I feel cleverer (which I never do), and then my lack of productivity depresses me, perhaps to the point you'd call "burnout" even.
Well, glad I'm not alone. Any tips on thinking my way around it welcome.