Could My Low Diastolic Pressure Be Causing Fatigue, Head Pressure, And Drowsiness, Especially In The Evening?

hi i have low diastolic going from 49 to 70 but its not unusual it comes down to 54 - 55 sometimes lower when i am sitting down it can happen on daytime and on evening on the evening it makes me tired and can fall asleep when talking to people or watching tv and gives like a pressure in my head that calms down if i lay down a bit but comes back after sitting up or stands up.