The setbacks have come from emotional toxin (huge family argument), or excesses stress (work projects) or physical activity (moving: packing and driving across America).
The big thing to watch for, I have found, are follow up crashes. If I crash once, it's REALLY important to be chill and not continue to push limits again for several days.
Two crashes, two days in a row... or 3 crashes in 4 days, etc... really set the healing back worse than anything else.
I used to be an hardcore mountain biker and snowboarder... clocking in many miles on high adrenaline-inducing double black trails per week... and not exercising has been hard for me.
The road back to it for me was slow.
I was able to start doing yoga immediately, and more intense stuff... like bike riding and kayaking after 9 months... in smaller doses.
I've found the worst exercise for AF recovery is "lifting" or strength training. The best is very gentle cardio (going on a morning walk)... and the mellow styles of yoga.
Smaller doses of exercise is a new concept for me... different than my old lifestyle and personality... which involved seeking adrenaline highs with marathon-like exertions. I had a "Warrior-like" attitude towards sports and exercise. Now I am learning to chill out and just enjoy moving about and the scenery. It's okay just to do a little exercise.
Over exercise can easily cause the adrenals to over-work and then crash... and my healing has been helped along fastest by avoiding overdrive.
Good luck with finding an optimal level of gentle exercise that goes well under your healthy maximum "limit"