I used to have sleepless nights caused by
thinking too much, until I learned what
caused it and stopped doing that.

It was caused by eating protein-rich
foods late in the day.  I believe this
is because certain amino acids are
precursors to neurotransmitters.
Eating meat, cheese, or eggs late
in the day may be causing a surplus
of neurotransmitters, leading to
excessive brain activity.