We don't know why. I noticed last week that he was kind of listless, so we gave him more vegetables, had him out of the cage more, etc. It didn't make a difference. Then, Monday night before I went to bed, I checked on him and noticed that he seemed to have wet tail or something similar. He hadn't had it the night before--I've been keeping a close eye on him--and since it was late at night my only option was to go get meds in the morning. Unfortunately, he was gone by then. Yaya is very upset, of course. He always gets upset when his pets die; we had to bury his betta when she died earlier this year. Poor boy. I tried to reassure him by telling him that Spike was sick and now he wasn't sick anymore and he got angry and said "he's not anything anymore, he's just dead." So I think I'll just leave that alone. He says no more pets from the animal shelter (where we adopted Spike) unless we know how old they are, and I think that's probably a good idea.
Goodbye, Spike. You were a good hamster.