Hi
@azizdhl, From my reading, not as professional advice or opinion.
1. My doctor told me that Blood pressure (BP) is often normal or high during a hypo because of the adrenaline released as part of the emergency response of the body to the hypo
2. I can experience low BP in hot weather. The blood vessels near the skin open wider and more blood pools in them than usual leaving less in the remainder of the circulation - leads to low BP, worse if I am on BP-lowering medication.
3. Australian Heart Foundation; Guidelines for the Diagnosis and Management of Hypertension in Adults 2016 quote an ideal BP as equal or less then 140/90, where 140 is the systolic, and 90 the diastolic pressure. (measured seated, with appropriate sized cuff, arm at heart level, slow deflation of cuff.
A 24 hour monitoring of BP is preferred to individual readings as a basis for diagnosis.
However
an optimal BP is quoted as equal or less than 120/80, with 138/88 to 120/82 as high-normal range. Hypotension (low BP) is defined in Wikipedia as less than 90/60. It is also usual to refer to hypotension where symptoms such as dizziness, fainting etc are present.
Orthostatic hypotension (lowering of BP with posture change e.g. lying or sitting to standing is defined as fall of 20 mmHG or more in the systolic BP (and in some definitions a fall of 10mmHg or more in the diastolic) +/- increase of 20 beats per minutes in heart rate. Some diabetics suffer from orthostatic hypotension as part of a complication called autonomic neuropathy.
4. Under guidelines mentioned in 2. above, BP monitoring during sleep is high if >120/70, compared to >140/90 when awake and upright. On that basis the expected fall in blood pressure compared to daytime when sleeping is only about 20 mmHG. This is not orthostatic hypotension (where the change is from lying down or sitting to standing). Unless there is a cause for sudden onset of low BP such as severe bleeding, the usual level of nighttimeBP does not cause coma etc. according to these guidelines and Wikipedia.
I hope the above helps answer your concerns and queries.