Ah, yes, I understand now. I think the first order of business is to take care of the Achilles tendinitis. Lots of RICE-ing (Rest, Ice, Compression, and Elevation), but it sounds like you've got that covered already.

I have a similar cycle with running and my mental health. I run to battle my depression, but if I get depressed, I have no motivation to run. Unfortunately, I got injured training for my last race, so I haven't been able to run since Labor Day, and the depression is coming back.

I was also a ballet dancer, but I quit training pre-professionally in high school. While I was living in the Midwest, I was taking some adult ballet classes fairly regularly before switching to yoga (a little easier on the body), but we moved back east and I just haven't gotten back into either activity. I completely understand the body issues ballet creates, and that was the exact reason why I was counting calories on Seroquel (and why my cousin warned me. And yes, I agree, I was extremely fortunate. It would have wrecked me otherwise).

What about investing in a stationary bicycle and a heart rate monitor? It should be easier on your joints (although, I'm not sure about the tendinitis). With a heart rate monitor, you can, well... monitor your heart rate to really push yourself while your riding to make sure your getting a good work out on the bike. If you have a bicycle you like, you could always get an indoor bicycle trainer. That way you don't need to buy a whole new stationary bike, and once you feel comfortable riding outside again, it's easier to store a trainer than a stationary bike. I'm wondering if the reason you gained weight riding the bike around town was because you were building muscle?

Please keep us posted!