"Two eggs a dozen", for example, recently lodged in my brain like a watermelon in a toilet.

Is there a word that generalizes these mental ticks, referring not only to onatomania and compulsive images, but also to songs stuck in your head and olfactory hallucinations?
Speaking of which, why are fake smells, of all these phenomenon, regulated to bad weirdness like epilepsy and stroke? Other mental ticks, like phantom phone rings, are so bizarrely common that they're written off to, "Dude ... workin' too hard?!", but phantom smells are just unheard of outside of serious problems. I mean, I've had some weird shit get stuck in my head, like I've recently been hung up on this observation: have you noticed, or is it just me, that some cars (when viewed from behind) lean to one side--but always to the left!?!? ... but I've never had a smell stuck in my head. Heck, I can barely even conjure up the memory of a scent, though I can recall all sorts of stupid trivia, for example, just off the top of head I can tell you that back in the mid-1970s scientists were stumped by the challenge of making fake banana taste.
But then there's "two eggs a dozen": stuck in my head like a watermelon in a toilet.
What gives?
(p.s., Thank you, once again, to WordSmith.org for stoking my bibliomania! The image, by the way, is from YouTube, but I'm not putting up a link here since this post is kind of gross and the video was made by a couple of kids.)