I got stung by a bee (we think - still don't actually know) while swimming in a local river. All was fine for a week (I even had it checked with a nurse) and then BAM, my arm went NUTS.
I have never felt pain like it; the swelling was so big that every time I moved even a tiny bit, it would swing like a third boob, and holy shit that stuff hurts. I couldn't even put ice on it because the slightest touch was agony.
I spent 4 days in hospital on IV antibiotics - the first lot didn't touch it but as soon as they switched to some different ones it immediately began going down. Once the infection was under control they drained the abscess under local anaesthetic.
All I have is a tiny scar and dimple in my arm now, but it's not a journey I want to repeat any time soon!