The uncomfortable swelling on the left side of the neck may be caused by physiological reasons such as falling asleep, or it may be caused by localized fasciitis, cervical spondylosis and other pathological reasons. 1. Physiological reasons: muscle tension and spasm caused by falling asleep or lactic acid accumulation in the muscles caused by overwork can cause discomfort and swelling on the left side of the neck. 2. Local fasciitis: aseptic inflammation of the local muscles and fascia of the neck due to prolonged head down and other bad habits or cold, etc. can cause discomfort and swelling on the left side of the neck. 3. Cervical spondylosis: cervical degeneration caused by cervical disc herniation, cervical spine small joint disorders and other diseases, the local nerve is compressed, the left side of the neck can appear uncomfortable swelling symptoms. The left side of the neck uncomfortable swelling may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.