I am having numbness on the left side of my head . it feels like the left side is sleep . what could be causing this?

Likely not serious: Most causes of head numbness, as contrasted to facial numbness, are benign. Commonest causes are compression/irritation of occipital nerve (sensory nerve to scalp only) often secondary to neck spasm or upper neck arthritis. Other common causes are vascular headaches (typically migraine). Facial numbness can be a symptom of actual or impending stroke.

Glasses?: Sometimes it can be sunglasses or regular glasses that are a little tight right over your ear.