I definitely confuse illness/a cold/the flu/bad sinus etc with being horribly depressed. It's hard to not be depressed when you feel sick, I just take it to the next level and believe I'm relapsing/I get suicidal.

As for hallucinations. I only had one experience after being on buspar for a couple days. For someone who regularly hallucinates, I don't know what the implications are -- whether or not being physically ill can cause your brain to respond that way.