As always, we are advised to give up/ cut down on alcohol intake, but this may not be relevant to you.
Alternatively, I came across a 'trick' that actually works.
If you wake up in the middle of the night, breathe in for four seconds (say 'one Mississippi, two Mississippi, etc to count seconds), hold breathe for seven seconds, breathe out for eight seconds.
Try it and let me know how you get on.