Is it so? It may could occur due to various reason ... when someone have eventful days or is stressed or troubled...During such times if someone begin thinking it may kick start the cascade of emotionally provoking train of thoughts which may cause hindrances in initiation of sleep.
Next Steps
My suggestion would be to follow simple SLEEP HYGIENE techniques ...it helps in majority of cases...and in rarest possibility if it doesn't work then do get enrolled for Comprehensive Insomnia Assessment
Health Tips
Sound Sleep have significant role in maintaining Health,immunity and wellness..