When tinnitus occurs in the left ear after lying down, you first need to identify the type of tinnitus, which commonly includes vascular pulsatile tinnitus and secretory otitis media. Symptoms of secretory otitis media often occur after an upper respiratory tract infection. After an upper respiratory tract infection, there will be a large amount of nasal mucus in the nasal cavity of the patient, and the patient will often blow his nose hard, so the inflammation will involve the middle ear cavity retrogradely through the eustachian tube, resulting in the accumulation of fluid in the middle ear cavity and thus forming middle ear infection. Vascular pulsatile tinnitus, which is consistent with the rhythm of the pulse, is related to changes in the patient’s blood pressure and abnormal blood vessel travel, and often appears or worsens when lying down.