Why do I always oversleep after I get back in bed after waking up at 5am? I fall into the deepest sleep and cannot wake up.

Stay up. I would recommend staying up. early morning is your most productive time. I would suggest staying up and reading or other productive activity. You may need to go to bed earlier to assure you get enough sleep. Most people need at least about 8 hrs. Some only need 6-7 and others may need 9-10, but more than 10 may make you more sluggish and less productive.