There may be many reasons one may find it difficult to sleep or go back to sleep if one wakes up at night.
I intend writing on a major reason for this first by quoting an anonymous source:
“One big reason why we don’t sleep may be told in just 3 words:
THINKING IN BED.
If we didn’t think in bed about the boiling thoughts of the day or didn’t think at all in bed we would sleep.”