In the sinuses there is a place which produces a lot of NO if you breathe through the nose. So the regular nose breathing also at night is crucially important for blood vessel width.
Second, the CO2 (carbon dioxide) is needed to release Oxygen from the red cells. As many breathe to fast and too much air the CO2 level falls and the Oxygen, O2 is not released properly.
Stress and fight and flight reactions cause high frequency breath, mouth breathing and loss of CO2 and loss of tolerance towards CO2.
O2 content in blood normally does not change much. 97-98% most of the time.
So O2 release and blood vessel size/width needs to be improved.
Every five to ten minutes practice 16 connected breaths at the speed of 5 sec. in continuously flowing into 5 sec outbreath and a possible pause until the next inbreath is needed.
This calms the sympathetic nervous system.
(6 breath cycles or less per minute gets you out of sympathetic stress mode)
ONLY breathe through NOSE!!
(This produces more NO, widens the blood vessels, blood flows better, lowers high blood pressure)
Practice holding of breath after normal outbreath often and often. (Continue only through nose!!!) ( This restores healthy CO2 levels and helps release the oxygen where it is needed)
Use mouth tapes or face former at night to avoid snoring and breath arrests which cause adrenal excitement and danger response and total fatigue in the morning.
Monitor your breath rate now several times and note it down. How is your breath cycle?
Seconds in? Seconds out? Pause?
Work on that ongoing for 7 days and remonitor.