twisted my knee snowboarding

Possible knee injury, or severe contusion?
Today I went snowboarding and fell very hard to jump from the right patella, just very Packed snow … no fun! I day and night for several hours and get home at this stage was clearly a little sensitive, but nothing to worry about. Now (several hours later) it hurts to stand, and if you accidentally fall up / contact / move the knee in any way that twists a little, the pain is terrible. It looks a little swollen and red, but nothing more. How do I know if this is just a bad stroke waiting to happen, or something else? Besides, what should I do? Thank you!
A I sound like a very bad blow. I ice and be careful.

