I think after the death of my uncle, it was after I watched Marley & Me
I've three labs and I absolutely ADORE them so that film tore me to shreds, even though I never cry watching films!
EDIT: Actually, I don't know how I forgot this one, but I was a major wreck at the start of last year after finding out that my best friend was facing jail-time from something terrible that he had done (something which took me MONTHS to sink in). I was a mess for months and it affected me greatly, so I was crying nonstop for weeks, and it filled a great gap when it came to conversations with my friends and family for a number of months before things started to look better again. But, thankfully, things are much better now.
I don't know how I nearly forgot that big part of my life - I guess my subconscious was trying to suppress it.