insomnia
"Was prescribed melatonin by my doctor about 2 months ago. Due to anxiety, and tinnitus I hadn't been sleeping until around 6-7am or not at all. Having university the next day was a big pain, when I had no sleep and had to be able to focus for the rest of the day. I had been on many different medications before for both anxiety and insomnia, some of which worked but all had bad side effects. 
Melatonin works extremely well for me, with no noticeable side effects. I take 2 mg two hours before bed, and it works well. I normally get a good 7-9 hours sleep when I take melatonin and don't feel drowsy the next day."