I open the window for fresh cold air. Then crawl under the duvet and close my eyes. If I'm lucky, I'll be asleep within two hours.
If I have the window closed, I will sleep, but wake up with a hangover. Even though I don't drink - its the dehydration, you see - I pour with sweat during the night if its too hot, can make me sick.
Dreading summer - the winter cold frosty air brings welcomed reief, and helps me get to sleep, but there's no escape from night-time dehydration in summer. Unless I want to be up to the toilet every hour from drinking so much water - and I do drink lots of water as it is.