My Son Clashed Heads With Another Boy While Playing Badminton.

my son clashed heads with another boy while playing badminton. My son ended up with a large egg size lump just above his left eyebrow but didn't pass out at the time but was very dizzy. This happened on Saturday. The swelling had gone away during the week.
Tonight he had a shower and the eyebrow swelled up again to the size it was when he clashed. Should I be worried? Will cold pack and panadol do>