Many people experience sleep problems every now and then, but how do you know when your trouble staying or falling asleep is cause for concern? The "rule of threes" can help.
In an article on middle-of-the-night insomnia (waking in the middle of the night and not being able to fall back asleep), Dr. Shelby Freedman Harris explains when to consult your doctor:
Occasional trouble staying asleep is quite normal and not necessarily a cause for concern. Sleep professionals like to use the "rule of threes" to figure out whether you should seek help. Consult with your doctor if the problem happens at least three times a week, with at least 30 minutes awake at night, and continues for at least 30 days.
By that time, you might feel so fried and exhausted that a trip to the doctor would be in order and hopefully you can get to the cause of your sleep issues.
What To Do If You Suffer From Middle-of-the-Night Insomnia [The Huffington Post]