Sounds like some sort of arterial blockage. Medical help seems the best option.

Like El Greko, I managed to step in a hole (deeper than my knee) a few weeks ago and strained cartilage, tendons, and attachments, as well as possibly bruising the cartilage in my left knee*** ... I sympathise, as my mobility is slightly restricted now too - as with you standing is actually easier than sitting... :-)

Actually very mild doses of Aspirin may help a bit - the old wives version is that it 'thinks the blood' - but doctors have big words for it... it will ease the pain when it kicks in too. You need to be careful if there is some vascular blockage problem that it doesn't let goo and start cruisng round the body looking to start some sort of heart attack/stroke syndrome.

*** Unlike George, I'm not a smoker... :-)