how will you know if your metabolism is messed up or not?

...

Just know that it is not. You can't permanently damage your metabolism. It rebounds within a few weeks or so after returning to normal eating. If you have lost some muscle tissue, then your RMR may be slightly lower, but if you regain that muscle, your RMR will be back to pre-diet level.

Go to your doctor and get your thyroid levels checked.

KJL

Well if you exercise moderately it won't be messed up.