Random torture

How to answer 'how are you' when you don't really want to talk about it? I cannot say 'I'm fine' as it is not true. However, if I say it is not fine, people will ask why and I don't want to explain. I don't want to get into details that still hurts me to think about it. But if I say 'I'm fine', the lie will consume me and will make me worse... Oh, the agony, it keeps insisting in being my best friend... What can I do to make it better when I got someone upset by mistake? Someone that didn't deserve at all? It was suppose to be an innocent joke, but I guess it wasn't. I said I am sorry, but it didn't feel like it sorted any effect. How can I make it better? My empathy, how to turn it down a bit? I hate hurting someone's feelings. Jokes are not meant to hurt, but they do sometimes...