Catching up on sleep is usually said in the context of "I'll sleep more in the weekend to counteract the negative effects of sleeping 4 hours a night during the

Catching up on sleep is usually said in the context of "I'll sleep more in the weekend to counteract the negative effects of sleeping 4 hours a night during the week". That is not how it works, since catchup sleep won't really do anything to reverse the effects of prolonged lack of sleep. You certainly will sleep longer when more tired, but it will not counteract the long term negative effects of sleeping too little.