The first thing that you should do is relax. I have had times where I cannot seem to fall asleep and that is because my thoughts are keeping me from sleeping. There is something, other than the fact that you cannot sleep that is bugging you. I find that I don't really know what it is that is bothering me until I tell someone exactly how I feel and slowly whatever is stuck in the back of my head, that I do not know at a conscious level, will come out. So the second thing that you should do is, talk to someone so you can vent. It is so important to talk to someone because it makes you feel 10 times better because you feel like you have support that can help you get over whatever issue you have. It also makes you feel a lot less alone and a lot less scared. If you don't feel like sharing it with someone, you can write it out. Once you address your problems they somehow manage to reduce and feel less scary.
Also, try not to focus on the fact that you haven't been able to sleep. I know what I am saying is easier said than done. But just try to focus on something else. If you don't feel sleepy, don't try to lay in bed and wait for sleep to come. Watch some television, or sit on your computer and watch YouTube videos, or maybe even read a book. When I am not sleepy and I keep waiting for myself to fall asleep, I end up staying awake for a long time. However, if I just let myself relax, stop thinking about how I cannot fall asleep, and start to watch something or do something else, I end up feeling sleepy and eventually can go to sleep.
If you still cannot fall asleep, it is okay! Do not worry. Just relax. Do not panic or become more anxious because that will not help you. Maybe visiting a doctor at that point will be a good idea. But if that is not something you want to do, you can always try sleep aid, which you can find at any pharmacy or stores like Target, Walmart and etc. Usually, if all else fails, I end up taking a little bit of Xanax as a final resort because at that point I know that my thoughts are beyond my control and I am going to need a little bit of help to calm me down and keep all the negative thoughts away. I usually try my best not to do so, but that's just because I am stuck on not taking any medication even though, I know I need to. So if you need to take medicine just take it. It's not worth the suffering. I am learning that slowly as well. I hope this helps you!