But I understand. I appreciate that finding a believable affliction first thing on a Monday can be a bit of a bogus ride for all you 24 hour party people, and that googling in the hopes of finding one is not entirely dissimilar to actually going to work in the first place. I get it. So, I've decided to help. Altruism I think they call it.
Below are a list of underused scourges of the body that are entirely original, believable, but most importantly, temporary. Road test one of these bad boys next time you wake up in a ditch on a school-day, praying like crazy for a head that wasn't the ill-gotten gains of some very questionable robot dancing. I know I will.
Smoke Inhalation. Particularly useful if your voice sounds like you've been at a nail gargling party hosted by Janis Joplin and Eartha Kitt.
Altitude sickness. More effective if you first grow a beard and make sure to magic marker a few digits before going into the work the following day. Remember not to give any credit to your Sherpa, as you will lose all plausibility as a mountaineer.
Love Blindness. Difficult to argue the viability of a day off work using this one, so be careful. On the plus side, it should clear up in a day or two; considering you can hardly even remember what she looks like.
The Sweats. A very real affliction apparently, which can be brought on by plane flights, diet allergies, and the two o'clock Monday morning realisation that you left the office unlocked all weekend.
The Runs. An oldie but a goodie. The greatest thing about runny poo is that no-one wants to talk about it, so make sure you go into excessive detail. Keeping in mind the common knowledge that no-one who wasn't genuinely sick would discuss the frequency and shade of their bowel movements, this technique should see you home and (figuratively) hosed.
Growing Pains. Nothing to do with calling in sick, I was just genuinely interested in what became of Kirk Cameron. I miss him.
Summer Sale Madness. You may need a bit of panache to pull this one off. My recommendation is to mumble the first bit, place emphasis on 'madness' and giggle uncontrollably during any conversation lapses.
The Bends. Take a snorkel to work the next day, and if anybody gives you lip, just get disproportionally irritated and reply: "Well I WOULD expect that coming from someone whose blood is oxygenated correctly!"