How to reduce 50 amp to 20 amp on the same circult?

My wife has a tanning bed that is 220, 20 amp service. I also just bought a spa that is 240 50 amp service. I thought I might be able to piggy back off the spa circult instead of running a whole new line. The spa is on a 50 amp sub panel.

I guess my question is, is there anyway to reduce the amperage going to the tanning bed if they are on the same line? I know we can't tan and use the spa at the same time, and the spa cycles at night, so we are good there. Could I run another sub panel off the 50 amp and circult and use a 20amp breaker?

I don't want to run another line as it's a pain in the arse. Any help would be appreciated...

thanks!