The photographs I have seen of people in bed in hospitals show them lying on their stomachs, with their heads slightly higher than their back, waist or legs.
They have people like on their stomachs to prevent the use of ventilators. If you are on a ventilator, it is doing the breathing for you, you are sedated to the point where you probably won't remember having been on one so it's unlikely at that point you'll be aware of anything. I just saw an interview with someone who spent 8 days on one and survived and can't remember a minute of it. It's pretty much an induced coma. So don't worry about this part of it.
Thanks, my only concern is that flat on their back is filling up their lungs faster and incubating the virus inside their lungs to proliferate even more, increasing the death rate.
I assume you know that they aspirate, as well as ventilate? It's not like a ventilator is a new machine invented for this crisis, medical professionals have been ventilating people with lungs full of liquid from causes like acute pneumonia for years, and long ago would have put to the test (a lot of tests) what physical position (of the patient) makes the ventilator best able to work. Reading stories about how little good ventilators ultimately do (though they sometimes save lives, the condition of the patient is usually pretty bad after the crisis) makes me doubly motivated just to do my best to avoid the disease. Nothing I've read suggests that there is much medical management that helps.
Trust the professionals, they know what they are doing. The lings filling with "water"is an issue known long before covid. As long as breathing by the patient still works, the back is rised as high as needed (even to 90 degrees) and non invasive ventilation is considered/applied. If this doesnt suffice anymore, the next step is taken and invasive ventilation after sufficient sedation is applied (the ventilator, you mentioned). During sedation rising the back of the bed is very dangerous and could cause circulatory collapse and CPR must be applied. That can be preventet using medication, which rises blood pressure, but it doesnt make the overall situation any better. So why endanger a patient. Please tell your mum, that the health workers may position you in any psoition they consider beneficial for you if you are sedated. Stay safe!