Hit my head... Concussion? Brain injury?

Today I was swimming and a rubber inflatable boat hit my head at fast speed. It didn't really hurt much, but it was a very blunt, hard blow. There was barely any pain. I was also able to immediately swim back to shore and answer questions with ease, and I remember everything before and after the event. I don't have any symptoms, though I do feel a bit light-headed right now but I think that's due to other things. This happened 12 hours ago. Do you think there was any damage done?