Is it normal to cry during sex

Ive had sex with my SO on multiple occasions and sometimes during it i feel like crying a little but never do, maybe the odd tear will escape but nothing bad but just before i just randomly started crying as though the worst thing you can think of has just happened. I have no idea why it happened. As soon as he realised he stopped, cuddled me, covered me up and calmed me down telling me im alright and its not my fault. Any ideas why this could of happened?