How are you supposed to go to the bathroom if you won't be taking any rest stops?
Since you'll have your own raft, you can bring a bag with tampons and a bag to dispose of your used ones in. Also, have a towel to place over your lap and wear loose shorts...and if the current isn't too heavy...
There's a lot of things I think you left out in your question.
Why were you at the hospital in the first place?
What was the IV for? Was it just for saline or a drug?
Why did you leave without signing the papers, and why didn't the hospital want you to leave?
If you are not under the influence...