Knee pain and swelling what could that be?is it considered serious should i be worried? any tips on how to lessen the pain and swelling?

Arthritis : The swelling suggests arthritis there can be many causes depending on your age: infection, crystals like gout or long term inflammatory arthritis you need evaluation.

Many things,: Swelling means you knee is irritated and it has gone into fluid production mode to try to lubricate itself as its only way to deal with irritation. You can have arthritis, a meniscus tear, gout, infection, acl injury, loose piece of cartilage, a tissue inflammation condition like pvns, autoimmune disease, etc. The list is giant. See your doctor.