The top of the neck is close to the body temperature control center. The thermostat system is nearby.
To sleep well, there should not be too much heat. That’s why it’s not a good idea to exercise before going to bed.
The cold, on the other hand, promotes sleep. If you have difficulty sleeping, place a damp cloth on your neck that you have put in the freezer during the day.
This feeling of coolness is very likely to help you sleep like a baby.