This is me. I am not exclusively IT but I am the unofficial IT department for my company (they don't want to pay an actual IT guy). I feel this across my whole job though. Phew, got that done, what's gonna happen next?
Probably they abuse me a bit. I know I'm good at my job but I get imposter syndrome in my head sometimes. $100k a year isn't awful though.
Sometimes I fantasize about dying and all the shit do and know and handle are lost and my coworkers can't figure shit out.
My last position had this problem. 'Silo's of knowledge'. We had a guy who could have retired yesterday who had so much institutional knowledge that when he left people were in such disarray. He was all, "I warned ya! You should have had me training people!"