Thanks for the details.
The dizziness or better known as vertigo in your case seems to be either due to postural hypotension that is a decrease (relative or absolute) in the circulating blood volume when standing up from a lying down position, this causes a delay in the blood reaching the brain when the person stands up from a lying down position due to a drop in blood pressure
and hence, causes dizziness or a feeling of blacking out.
The other thing that comes to mind when there is a lack of other symptoms is benign paroxysmal positional vertigo, which is a condition of the inner ear canals. The canals are filled with fluid and are responsible for maintaining balance by shifting of this fluid. These canals develop small microscopic calcium stones in BPPV which shift and affect the fluid balance in the inner ear, this can cause positional vertigo like the one you are experiencing.
The treatment for postural hypotension is by medication as well as by alleviating the under lying cause and the treatment for BPPV is by a maneuver known as the Epley's maneuver which can be done in the physician's office and relieves the BPPV very effectively.
I suggest that you get an appointment with your PCP at the earliest to have these issues addressed and for a comprehensive workup.
Hope this helps.
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