A sleep study is a test that measures how well you sleep and checks for sleep problems. For some sleep studies, you stay overnight in a sleep lab at a hospital or sleep center.
In other cases, your doctor can give you a portable sleep monitor to use at home, so you don’t have to spend the night in the sleep lab

Before you go to sleep, a technician attaches small, sticky patches called “electrodes” to your head, chest, and legs. He or she will also place a small tube beneath your nose and might wrap 1 or 2 belts around your chest.
Each of these items has wires that connect to monitors. The monitors record your movement, brain activity, breathing, and other body functions while you sleep.
If you have a history of trouble falling asleep, your doctor might prescribe a medicine to help you fall asleep in the lab

Your doctor will order a sleep study if he or she thinks you have obstructive sleep apnea
The main symptoms of obstructive sleep apnea are:
loud snoring,
tiredness, and
daytime sleepiness.
Other symptoms can include:
Restless sleep
Waking up choking or gasping
Morning headaches, dry mouth, or sore throat
Waking up often to urinate
Waking up feeling un-rested or groggy
Trouble thinking clearly or remembering things

On the day of your sleep study, you should:
Avoid alcohol
Avoid drinking coffee, tea, sodas, and other drinks that have caffeine in the afternoon and evening
Take all of your regular medicines, unless your doctor tells you not to.