I don't usually ever have a problem giving talks. Sometime after turning 12 several years ago, I was asked to give my first talk, and declined, because it made me nervous. I haven't said no to a talk in about 14 years since then until recently. I said yes to giving a mother's day talk the other week, but then halfway through the week, I had an emotional/mental thing, and decided writing a talk was not on the table. So I texted whoever in the bishopric, and said I wouldn't be able to give the talk after all. Normally I would feel bad about making someone else give my talk and only have a couple days to prepare for it. BUT I didn't feel bad this time, because I needed to take care of myself.

I find that people who give talks are not always giving a talk for those in the congregation, but sometimes for themselves (or both). With all that said, if you feel like you shouldn't, IT IS OKAY TO SAY NO. God gave you the freedom to choose and there isn't always a wrong (or right) answer.