Suspension trauma is a perfectly natural reaction caused by the body being held in an upright position. It will happen to everyone, and you do not need to be ill or injured – simply standing still and unable to fall over.
Our blood supply and heart cannot cope very well with standing up – gravity pulls blood into the tissues of our legs, and the heart cannot suck it back. Eventually, if enough blood pools in the legs, we will faint. This is fine, so long as we fall over – the blood all rushes back – but if we can’t fall over, then we die.
sometimes we faint. If we can’t use our legs at all, such as if we’re strapped into something or hanging in a harness, then we will faint. The problem comes after that – if you faint, you really need to fall over right away. Stay in the same position, and your brain has no oxygen supply.

Anyone who could faint and not fall over. People working in industrial harnesses (using abseiling or fall arrest systems or people in confined space shafts), people using harnesses for sport (caving, climbing, parachuting, parascending, bungee jumping rope access) and people using harnesses for special tasks (stuntmen, theatrical flying, etc Me}) are all exposing themselves to high risk, some more than others. Anyone who is secured to a vertical surface for any reason (a rescue litter or spine board, plank of wood, door, bondage equipment, etc) may also be at risk. The most famous, or infamous, example of deliberate suspension trauma is of course nailing someone to a cross.
In any of these situations if you are not using your legs for support, or are unable to move them, then you will eventually faint. If you live or die depends simply on how quickly you fall over – preventing that from happening will of course kill you.

Now to get that blood back up from our feet, we could increase the pressure – forcing it round like a blockage in a U-bend – but that would need such high pressure our hips would burst. No, instead of turning up the power, we have evolved a much better solution – hearts in our legs. Yes, you read that right. The veins in our legs already have one-way valves in them, so all we need is to squeeze them and we’ve got ourselves a pump! Since we started walking upright, these leg veins have moved so they are buried in between the muscles, so as we move our legs and walk about, the veins are squashed and released over and over – pumping the blood back up into your abdomen. It’s an amazingly good system – when you’re running, there’s hardly any blood pressure in your feet at all!
Of course you can see the error with this perfect plan – if you don’t use those muscles the pumping effect stops and your brain, right at the top of the pile, runs dangerously low on blood very quickly! This can happen if you’re standing very still, or hanging in mid-air, or strapped to something. If you’re standing still then the brain can fix the problem…
Firstly, when blood to the brain reduces, your brain decides to put you in shock. You must be bleeding somewhere, right? So, it increases your pulse and breathing rates, you feel a little sick, shivery, cold, sweaty and anxious. This doesn’t really help much, as what you SHOULD be feeling is a craving for exercise – but never mind, evolution is never perfect. That higher pulse rate shunts blood up to the brain and away from the skin, which helps for a few minutes – but of course it’s still pumping blood down into those legs as well. Eventually, your brain realizes its mistake and goes for plan B – the Central Ischaemic Response. You faint.
Why? Because of course if you faint, you must fall over. Your brain has learnt that from millions of years of… falling over. When you hit the floor, the blood trapped in your legs returns, and all is well. You wake up, feel sick, and if you’re a soldier on the parade ground you prepare for the punishment of your life. The problem is when you don’t fall over. Your brain has no comprehension of that idea – so if you are physcially held upright after you’ve fainted – by a harness, litter or cross – your brain is in deep trouble. It’s turned off its own blood supply to get you to faint, and it still needs the blood in your legs. So, it waits. You’re unconscious of course, so you aren’t aware of all this.. but you wait. You do not ‘wake up and try something else’ – you wait. You die waiting.
How long have you got?

If your legs are perfectly still, then you can start feeling the first signs of shock in as little as three minutes. The average is between five and twenty minutes. You will faint a few minutes after that, and if you are not allowed to lie down straight away then your brain can start to die a few minutes later.
So, worst case scenario you can be dead in ten minutes. Actually, less than that – because once you faint, you lose control of your airway and if your body is upright you can choke on your tongue and suffocate in a matter of seconds.
Not everyone will be pushing death inside of a quarter hour though – the time it takes is random. Some people will last ten, some sixty. Age, height, weight, fitness, sex, race – none make any difference. The same person will react differently from one day to the next. In short, it’s unpredictable. Very old people suffer first, as their muscles are less able to control the blood flow, and very young children are immune as their bodies are just too short! Nobody’s sure at what age you become ‘at risk’, but certainly anyone over about 5 feet tall is capable of feeling the effects.
Luckily, we’re telling you all this because there are

but its so important when yr lowewred down to be kept in the w postion