insomnia
"Insomnia started years ago due to ageing. Tried several sleep aids then settled on just 1/2mg Melatonin nightly. Gives me 6-8 hrs sleep including REM. Often remember dreams; like watched or created 3-4 different movies in my mind i.e. REM every 2hrs.

Would give Melatonin a 10 except every 2 wks or so it  stops working. Tried increasing dosage at that point but even going up to just 1mg gives me neurological twitches. 

For me, a retiree, what works is 2 wks 1/2mg alternating with 2 wks of zero sleep aids, tolerating sleeplessness. 

Beware of doctors who offer to replace Melatonin with things that will fry your brains while sparing your heart.

Melatonin does not directly induce sleep; it can nudge your body's natural melatonin production."