You're best cure for insomnia? It's very early, going to work in a few hours.
If this is a one-time thing and you can't sleep tonight there isn't much you can do at the moment. I can tell you some tricks to falling asleep tonight but they will only help you so much.
You have to have your body and environment set up correctly to make it easier to fall asleep. After that is calming your mind which is the hard part for me at least.
Environment:
Block out all light if possible.
Reduce the temperature if it is warm, I shoot for 68-70 degrees (20-21 C)
If there is noise turn on a fan or look up a white noise app, or search on Youtube for something like sleep rain or delta waves or sleeping music
Clean sheets and a made bed always make it easier to sleep - make sure you remove any anxiety you may have about your bedroom
Body:
Look up yoga exercises for sleep
When you lay in bed make yourself comfortable and then consciously think about your body parts feeling relaxed as if they are going to sleep, start with your toes and work your way up to your head
Don't move about, try to be still
Plug your right nostril and breath through your left, deep breaths - 3-4 seconds in and 7-8 out
Take deep breaths in general while trying to calm your body
Mind:
Meditate to clear your mind if you're into that
Lay awake with your eyes open and repeat "I will not fall asleep" (weird trick that makes you really sleepy - try to keep your eyes open!)
Do mental math if you have distractions, this one kind of works for me but I've heard it working for others
Don't think about things directly related to your life or you will interject yourself into the thoughts and pull yourself back to real life - this can keep you up for hours. Instead, try to think about something unrelated to yourself/your life
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To sleep better long term:
Go to bed at the same time every day and wake up at the same time - even on the weekends
Exercise - this is a really big one especially for people in our industry
Obviously caffeine and other stimulants can affect your sleep, avoid these starting 8 hours before bed
Get into a routine, this can involve certain things that you only do before you fall asleep, putting on a hand lotion that smells only before you fall asleep can tell your body that by smelling this thing it's time to sleep
Try not to nap during the day
Don't do anything in your bed but sleep and sex
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If you have to sleep and you know it will be an issue and you need something to rely on then get some Melatonin. DO NOT rely on this for day to day use. It should be something that you use here and there. You can also use it to fix your sleep schedule, just make sure you only take it for a couple of days in a row and you may even want to ween off of it by cutting it in half and then a quarter the last two days.
Melatonin occurs naturally in the body so this is a pretty safe thing to do but like anything else use it in moderation.