Nightmares of an Insomniac

So lately I've been having a ROUGH time trying to fall asleep at night. Sure, it could be my bumpy mattress that's been long over-due for an exchange. Could be the abnormal sleeping patterns that come with the job (of being a university student, that is). Ooor, as my Mama is quick to point out, all that candy and sugar I consume throughout the day have gotta be bad news. But maybe, just maybe, its something else...
I find that lately I've been utterly consumed by some recurring thoughts. Call them an insomniac's nightmare. They pop in throughout the day, but are quickly replaced (thanks to my unusually short attention span) by whatever's occupying my absorption at the time. It is only when I'm laying in my uncomfortable bed, in the pitch black emptiness all around me that they are given free reign, and thus are able to immerse me wholly, beckoning me into their dark world. I guess it should be quite obvious by now that these aren't the cutesy, "lemme mentally pick out tomorrow's outfit" thoughts, nor are they simple reflections on my day.
No, these are the ugly thoughts, full of doubt and despair. Their creator continues to agonize me, reminding me that there is plenty more where ever they came from. They're like an all-consuming smoke that drifts into my nose, up into my brain, and is able to pluck all the apprehension and distrust in myself and multiply it, while simultaneously spreading it like a plague. 
Sometimes they're ambiguous thoughts, filled with "what-ifs", and "maybe I wont do ---  after all", but no matter- they all lead back to that same ugly, repulsive creator. Sometimes they're more assertive, scolding me for things I have aspired to do, or dreams I have somehow created for myself. They prick and prod, and every so often I'm slapped by their distant cousin, reality. She's the real bitch, using the waking world to her advantage- images and words from real people in my life to ridicule me and "remind" me that beyond this, there lies nothing else.
Do they sell some sort of bottled cure for this kind of insomnia? Can they prescribe a medication for self-doubt?