I've just been told i have hematoma, should i be concerned?

Location, location..: A hematoma is simply blood which has collected outside of a blood vessel, no different than a "black-and-blue" mark. The critical issue is where this collection is. If it's sitting under the skin, it is of no concern. If it's between the skull and the brain, it can create pressure on the brain and be life-threatening.

Location and cause: Hematoma is a collection of blood, as most people see after.Local injury these should resolve over time if no bleeding disorder (platelets, anticoagulation, hemophilia). The problem is when is inside closed space like skull or spine. Here it can increase pressure on soft structures (brain, spinal cord) and cause damage or death. If in muscle, can cause compartment syndrome.