My up drain just fell out. I am still pushing out a lot of fluid. What do I do?

First of all, don't panic and don't rush off to a possibly expensive and unnecessary ER visit. Call your doctor first. Waiting even a few days shouldn't cause any real harm. 
Fluid build up in a surgery site is normal- it comes from the tissue surfaces leaking fluid to cushion and clean themselves as they heal. We call this a seroma. Once the tissue has a chance to heal and seal itself back together, the fluid decreases and the body eventually resorbs what it made. If there's a lot of fluid at the surgical site and not a lot of coverage between the fluid in the incision, sometimes the fluid can make its way out of the incision and leak through the skin. This isn't dangerous, but it can be messy. Ideally, we like to wick away the fluid with a drain to allow healing tissue surfaces more opportunity to be in contact with one another and stick together. If the drain was removed before the tissue site was dry enough, sometimes fluid can re-accumulate in the surgery site. This is usually easily solved by draining the fluid with a needle or placing another drain with ultrasound guidance. Sometimes if the amount of fluid a small enough, simple watching and waiting will allow the body to absorb it and eventually it will go away. If the area is incredibly painful, swollen, and very red, or if you have flu like symptoms or fever, there can be infection at the site. This should be evaluated by your doctor soon as possible.