How often should one shower if they spend all day in bed (except for preparing food and using the bathroom)?

I think from a health and smelliness standpoint you could certainly shower every 2-3 days on that schedule. Supposedly most of us shower too frequently.

But getting clean, because it makes us feel good, counts as self care... which is one of the best things we can do for our depression. So I'd say maybe keep on with your normal shower routine rather than continuing to spiral. And maybe think about talking to a professional about your depression. There *are* treatments and therapies that legitimately work, though it doesn't always seem that way when you're down in the dumps.