Need help recording myself sleeping

Hello folks,I am 18 and wake up everyday feeling very exhausted. So before I go for a sleep study,I want to record myslef sleeping as a proof and also to find out the cause. So pls tell me some jugaad I can do with my phone. Ya some cameras as well which can record for 7 hours straight.Low light vision and sound is not necessary. Also need to do it for only 1-3days,so want to go as cheap as possible. And one more thing,pls suggest some somnolgisits or doctors for the sleep in Mumbai.