How do we know that we aren’t sleeping and that we aren’t in an alternate universe?

Question: How do we know that we aren't sleeping and that we aren't in an alternate universe?
- Keywords:
  alternate,
  sleep,
  universe
Asked by 655frah46 on 7 Mar 2017.
- anon answered on 7 Mar 2017:
  
  I am not sure about you but I get dreams when asleep. If we were in the alternative universe, I highly doubt we would be leaving our brain behind stuck in the dreams from the universe. I won’t be getting any dreams if I were in an alternate universe. It’s probably not the best answer, but there’s a reason why I chose to be a biologist 🙂

Question: How do we know that we aren't sleeping and that we aren't in an alternate universe?