I have had a knee injury for 10 months and have been told to ice my knee whenever it gets sore from PT or exercises. Today, I iced it for 20 minutes (the same amount of time I normally do), but this time shortly after removing the ice, it swelled up, became extremely stiff, got hot, and developed like little divots in certain areas. The heat and divots have faded, but it is still stiff and swollen. Why did this happen and is there anything I can do about it?