I was bitten by a spider (two small fang marks) on the top of my foot last evening (app. 12 hrs ago). Did not see the spider. There is a little redness, but the main symptoms are pain in foot when I walk, and my entire leg, up to thigh, feels strange. Almost a numb feeling, a bit of tingling . It feels tight and I am just aware of my leg, if this makes any sense. Should I be concerned?