No, even though I do get some headaches from time to time, they aren't the life-altering migraines that some other people suffer from. They're the type of headache that gets better from sex.
I sometimes don't feel like it - if I have a kidney stone, or am feeling ill from something else. If that happens I just say what the deal is. Usually though, when I don't feel well, my man knows and assumes sex is off the table and he doesn't want me to feel pressured to be with him when I don't feel well. So if I want to have sex when I don't feel well I'll actually just tell him. Then he gets all happy and excited. lol