Yesterday, I noticed a large swelling on the top of my foot / front of my ankle. It's like a large fluid filled lumpy thing.....quite 'puffy'. There is no pain at all, even if I prod it. Got up this morning and, although it had gone down somewhat, it was still there. Anyway, just done the Fernwood 5k and it's swelled right up again. It's very noticable but, again, no pain. Any ideas what it could be? I've never had anything like it before.