If a bad tooth is left untouched by a dentist what could happen?

What problems can it cause?

I keep it clean and brush my teeth several times a day and use listeriene it doesn't really give me any trouble maybe 4 or 5 times I've not got abses or anything like that
I hate dentist and I know I'm not on my own but I mean I freak out start shaking and heart pounds in my chest till I feel sick. I've made an appointment to get referred to the hospital to get it taken out was just wondering if it could be making me ill I've had several serious chest infections and cold after cold after cold and other things. Could a bad tooth cause anything else?? Head aches migraines,neck ache