Everyone tosses & turns many times during the course of a night's sleep. This is natural & healthy.
Uncomfortable pressure points cause the body to shift during the night while you are asleep. However, the wrong mattress can cause uncomfortable pressure points causing the body to continually shift throughout the night disrupting deep, restorative sleep.
Apart from disrupting your sleep pattern, continual tossing & turning also uses up a lot of energy; not in the least helpful at a time when the body is trying to rest & revitalize. That is why, on occasions, you may wake-up in the morning feeling even more tired than when you went to bed!