I have read of it being a drug that can form dependence, as your body will produce less of it due to it being supplemented (I haven't done a deep dive to confirm that with scientific papers, but it certainly sounds plausible).

This article advocates for micro dosing 100 to 300mcg of melatonin, and anecdotally I have found it to be quite effective.

It mentions offhandedly that if you overdose on melatonin for long periods, as you appear to have done, it'll "take days before your brain goes back to normal." But it's hard to say how long it would actually take for your sleep to resume to something approaching normal if you went cold turkey or microdosed for a length of time. It's possible you may want to use some other form of artificial sleep aid temporarily until your body responds to the correct doses of melatonin.