I have a swollen knee after recent impact, will the bio-magnetic mat be helpful?

If you have a recent acute joint injury, it should not be heated for the first 48 hours after an injury or until the inflammation and swelling subside. 

If you have a joint or joints that are chronically hot and swollen, these joints may respond poorly to vigorous heating of any kind, but you may still use photon (red light) or bio-magnetic PEMF therapy.