This totally calls for a "your mom" joke, but I'll be a good boy and keep on-topic...
I once was bitten after dark by an unidentified insect while on a mountain trip, I managed to kill it, but it hurt like hell and when I tried feeling for the bite, it felt like a massive bubble with some leakage, so I got afraid of an allergic reaction and stuff... Then I woke up in the morning and it was completely gone, the only evidence it hadn't been a dream in the form of mangled remains of the culprit lying next to my bed...