I think you have just described normal life. It's okay to be down. Either that or I'm just as messed up as you and don't give a darn anymore, lol!
Coffee made me stable, but it was a stable cranky-pants, chest-pain mode. I'd rather ride the coaster and enjoy the mountaintop days to the max and then bask in the mud of anxiety-free depression here and there. Heck, I know I get some seriously good relaxation done when I'm on the downside. LOTS of people are embracing emotional lability lately, as long as it fits into your life and you're not going to end up naked drunk downtown urinating on police officers.
My wife and I BOTH regularly fly up and down, and we've learned how to interact with each other in every phase except when we're both extra cranky. But even if we do get on each others' nerves, it's only a few minutes before we both realize what's going on and just remember to relax.