My question involves labor and employment law for the state of: Washington

I am an employee of Fedex. My shift started a 230am and I ended up calling in at 530am. Usually we do not get off until around six and I know most employers wants notice hours before work. The reason why I called so late was because my grandpa went to the hospital the night before and I took a nap in the family lounge so I could be awake for work. No one knew I had work and I set my alarm but ended up sleeping through it. At Fedex no call no show counts for a warning letter and I already have two, on more and I am toast. When I called the manager at the time he said to bring documentation to prove I was at the hospital. I asked the receptionist and nurse if they would write me a note but they had no clue what to do. I do not know how to provide prove that I was at the hospital for someone else. What should I tell my manager or do to prove this so I do not get hit with no call no show?