Haven't read all the answers, so sorry if I repeat something.
I often get that when I have a lot on my mind. It was awful when Wiz was first in the psychiatric hospital and again right before and for a few months after I made him leave. I used a combination of things. A soothing evening routine - warm bath or shower, cup of Celestial Seasoning Tension Tamer Tea, often a guided meditation tape or cd to listen to (we have some that really help me get to sleep). I also kept a pad of paper and a pen or pencil right next to the bed. When I would wake up in the night I had all these thoughts and worries whirling around my brain. I would not try to not think of them. Instead I wrote them down so that I would not forget and I could then think about them the next day. That was hugely helpful because otherwise I worried I would forget whatever it was. I would restart my meditation or audiobook and then could get back to sleep.
melatonin is also helpful. The tea I mentioned is sold at Walmart, Walgreens, anywhere that they sell tea pretty much. It is a very soothing blend of herbs that is really effective to help yourself calm. Tazo Teas also makes and excellent tea for calming yourself. It is called Calm Tea and it tastes more like health food than the Tension Tamer. It is also mroe expensive but not really outrageous. It is even more calming because the blend of herbs in it. I found out about it from a fibromyalgia group and most of us have problems with sleep and getting good sleep, plus problems with anxiety. I don't really like the taste (I do like the taste of tension tamer even with-o honey or sugar) but it isn't terrible. (I really abhor anything that tastes even remotely like health food so that is actually praise from me, lol)
One of the great things about the Calm tea from Tazo is that you can buy it by the cup at many Starbucks. So you don't have to buy a whole box. If you like it and/or find it effective - don't buy the box at Starbucks. Their price is outrageous by the box. Many groceries carry it or you can get it online substantially cheaper. Then if you have a couple of tea bags in your purse you can just get a cup of hot water for free and use your tea bag. Altoid tins are perfect for carrying tea bags. If I drink several cups of either tea in the evening I have a much better chance of sleeping through the night (long as I don't drink more than 1 in the hour before bed, Know what I mean??)
I hope this helps. If you don't have meditations or audiobooks, try classical music.
If you need more help, try melatonin or even benadryl. If you take benadryl (the ingredient in tylenol pm, advil pm, and many other OTC sleep aids) it is a good idea to take a mucinex with it. The instant release generic version is fine because it lasts about as long as benadryl (4-6 hours).