The history is very typical of Postural hypotension
Your blood pressure drops suddenly while standing and this is causing dizziness
Your need to record you blood pressure standing, sitting and lying position.
More than 20 mmHg difference in the systolic pressure is suggestive of Postural hypotension.
In that case do the stand up suddenly from the bed.
First sit and come to the edge of the bed and stand up slowly.
Do consult your doctor for more information.