Your knee is sort of encased in a sack. The swelling is pooled blood. That’s why you should keep it elevated as high as your heart as much as possible. Ice 20 minutes on, 20 minutes off. Don’t use heat. That’ll just make the swelling worse.
The blood will get reabsorbed on its own. One of the times I fucked mine up I actually had it drained. The doctor shoved a big needle to what felt like the middle of the joint and sucked out like 100ml of blood, which was almost half of the blood pooled. It felt better, but hurt like a bitch. Not worth it. The other two times I just waited for the swelling to go down on its own.
Aside from the pressure, does it hurt to bend? If so, that’s probably good because it’s probably just a bruised or slightly torn ligament (read: sprain.)
A torn meniscus or broken articular cartilege doesn’t really hurt to bend, it just bled and swelled a lot, locked my knee sometimes when the chunk got in the way. I remember riding the bus home from school one day after the 2nd time I fucked it up. We weren’t positive that I needed surgery. Then I felt a chunk of cartilege the size of a thick quarter floating under the skin in my knee. Fucking creepy feeling. It’s actually called a joint mouse, because it’s akin to a mouse running around under a carpet like in Looney Tunes cartoons. I got off the bus and had my mom call to schedule the surgery. All just arthroscopic though. In/out in one day.
So yeah, stay off it as much as possible. Ice 20 minutes on, 20 minutes off. no heat. Keep it elevated. Then once it gets better go easy on it for a few months. If it gives you chronic problems or if you can’t get to the point of walking comfortably quickly then it’s time to see an orthopedic doctor. You may have torn something that needs repairing.