Yes, it is very "normal" for depression to be a roller coaster. But, if you have been getting good therapy and good meds, no doubt you will be more resilient than you were before and probably bounce back faster to a better state.

Do relax if you can--do some deep breathing or take a bath or warm shower. Listen to music that pleases you. Maybe write down some of your troubling thoughts in a journal, to air them out.

Sometimes I think it's unconscious things that trigger a "relapse" to a sadder mood. But it can pass or lessen, just as it did for you before. Don't give up...it WILL get better again.