Missing commitments

Is it ok to not go somewhere (ie voluntary work, college) if you are not feeling up to it? Its just Ive had anxiety for years and its gone a bit now so im getting into a routine, Im supposed to do voluntary work on tuesdays but I don't feel up to it and feel that if I go in I might feel worse and panic or something, no one will know but I just hate it. Im worried though that if I miss things because of this it will become a habit and how the hell will I hold down a career? I will have to go in then even when I feel like this, Im also worried that I sometimes confuse the feeling off/anxious thing with lazyness, where is the line drawn?

Of course you can miss it if you inform the people involved beforehand.
I get anxious about strange situations like volunteering but I've found that it really does help you overcome the anxiety once you get into it.

Last year I'd never have thought I could help at a playscheme from 9-4 in the summer, let alone enjoy it, but it turned out to be one of the best things I've ever done and now I'm training to be a mentor in high schools, which is completely different to my degree.

I'd suggest going a few times, you might find that it's really beneficial.