I knocked my fore head about 4 weeks ago and had a small bump. today i felt a tingling burning sensation and the long bump dropped to become a lump ?

Hematoma: The lump and bump is a blood clot under the skin. This slowly resolves as it breaks up gradually. Black and blue skin color usually follows. The tingling sensation is an irritation of a superficial nerve in the skin and is not within the brain. As long as you're not experiencing ongoing headaches,dizziness,visual difficulties or vomiting, you don't require a physicians examination at this time.

Difficult to say: Not entirely sure I understand your question. Sometimes as part of the healing a bruise will clot off then shrink and as it shrinks down/resolves change shape. But difficult to be absolutely sure this is all that is happening and so best to see a doctor here for examination. If I've misunderstood you feel free to repost/rephrase the question/clarify