It's not good to use someone else's prescriptions.
Heather can't sleep because she is worrying about a big exam she has to take in the morning.
Heather wants to get some sleep.
Heather makes herself a cup of hot tea and then reads a book until she falls asleep.
Heather takes one of her mom's prescription sleeping pills to help her sleep.
Heather has a good sleep and wakes up refreshed and ready for her exam.
Heather feels groggy from the sleeping pills and can't concentrate on her exam in the morning.