When is a head injury serious enough to see a doctor?

I was bending down last night to feed the cat in a new house and I hit my head on a hockey table on one of the steel things that sticks out. I put ice on it for twenty minutes and took advil. I slept for at least 10 hours. Now I have a very large and noticeable bump over my right eyebrow. I feel groggy but managed to drive just fine. Are there any telltale signs for a concussion or a closed head injury?