When you're in a bad mood, do you appreciate when people reach out to you (phone calls, emails), even if you choose not to talk, or do you want to be totally left alone?

depends who. i hate making a small talk then, but liek talking with my good friend, even if i choose not to delve into the cause "i feel terrible now but have no strength to even talk about it"

....

It depends on what type of bad mood. Usually I don't mind someone just asking "is something the matter?" and then dropping it more than once usually annoys me and i appreciate it when my best friend "reaches out"

Depends.