Is it normal to still feel exhausted weeks after coming back from burnout leave?

I took six weeks off work for burnout earlier this year. The time off helped, I felt almost like myself by the end. But I've been back for about a month now and I'm tired again by Wednesday, not the panicky kind of tired from before, more like a heavy flat feeling. I've cut my hours slightly and I'm seeing a therapist every two weeks. My manager has been understanding. I guess I'm asking people who have been through it: how long did it take before your energy felt normal again? And was there anything that helped more than you expected?