I experienced a strange side effect when experimenting with melatonin: My vision degraded as if I was having a migraine. I experienced tunnel vision and color

I experienced a strange side effect when experimenting with melatonin: My vision degraded as if I was having a migraine. I experienced tunnel vision and colorful artifacts without the headache. I can't say with 100% certainty that melatonin was the cause, but there was a correlation... and I have not experienced the problem since I stopped taking it.