Drains are a trial Lisa. I leak for weeks but not everybody does, it is quite common for some people to dry up in a very short time.
A couple of things can happen to drains, they can get blocked or lose suction. If your little 'bulb' above the actual bag still looks like it is slightly collapsed, it still has suction, in which case it is still working, you may have just stopped oozing. The end of the drain looks a bit like a soaker hose -- lots of little slots, so it takes a bit to block them but it can happen. Sometimes blockages resolve themselves, a gob of muck gets sucked through and everything keeps going.
If you are still unsure with it in the morning go back to ED. There will be a different lot of staff on so you may get better advice.
If it has stopped working, it is not the end of the world. At worst you may have to have it replaced, at best your surgeon may adopt a wait and see attitude as you may have just dried up. Keep a really close eye on your temp until you can connect with your surgeon or BC Nurse;, the fluid will be fine for a day or so sloshing around in there ( you may get to learn about seroma) as long as you don't get an infection. You don't want anyone who doesn't know what they are doing tinkering with it. F%#@, I'm just making this worse, aren't I.
This shit always happens on a weekend. Or a public holiday.