Another mental exercise that has been known to lull the mind into a state of sleep is Word Scrambling.
Word games are a great mental exercise for falling asleep, because they are entertaining enough to enjoy, but not stimulating to the point of keeping you awake.
The word scrambling technique used here is sort of like playing a mental version of the board game "Scrabble". You visually take letters from one part of a word and you swap them out with new letters in order to create a different word.
The technique works best with 4 letter words, but if you are really clever, you may be able to do it with longer words.
Word Scrambling (Step-By-Step):
Turn off or dim the lights. Remove any noise distractions from the bedroom.
Choose a word that is 4 or 5 letters long.
Transform that word into the other word by changing one letter each time.
So for example, if you chose the word "WAND", you might change it into the word "MELD".
You would swap out one letter at a time, like so:
WAND = WEND = WELD = MELD
Continue converting words into other words like this over and over until you lull your mind into a state of sleep.