What Causes Sudden Blackouts With A History Of Hypertension?

Dear doc, my father 62 year old, Driver by profession has been experiencing sudden blackouts in the evening or ant night, while in the sitting posture, which lasts for about 1 minute. I am worried as cud this be am immenent CVA or TIA can u please suggest me some differential diagnosis for the said condition. He has a past history of hypertension and was a chronic smoker but not now. No history of diabetes but has allergies to dyes. Kindly help