That is most probably a lipoma..

Cyst at back of head usually are dermoid cyst or sebaceous cyst. Any cyst usually are asymptomatic and don't cause any harm until & unless they are infected or big enough to cause neurovascular compression. If you don't want surgery, then there's nothing to do because there's no medical treatment for cyst. If you are bothered for the swelling then treatment is surgical excision only.

Go for a consultation. Physical consultation is better. Need not panic. Get it diagnosed. If needed, a minor surgery will be done as a day care procedure

Usually the cysts arise due to block of sweat gland duct. Pls meet a surgeon, get examined and you will need a minor day care surgery to get cured. Do send the removed tissue for biopsy

Kindly share pics Likely lipoma or sebaceous cyst Visit a Surgeon for evaluation

Mostly it will be sebaceous cyst or lipoma. A clinical examination will give better idea. It might require excision or may not.