Sleeping with magnets

I slept with hardware store magnets wrapped around my knee for the past three nights. I read that magnets might alleviate the pain and swelling, but the relief is more marked than I could have hoped for. Since the swelling is as grotesque as ever, I suspect a placebo effect, yet I should think that a placebo effect would require that I be deluded, but how can I be deluded when I can see the swelling in my knee and fully expect it to hurt?