I can see people talking about 3 completely different things here. I say that as Ive had them all and they were different including paralyses.
I had paralyses during the time I was bedridden for 9mths. It was scary and I honestly thought I was going to die. The paralyses must be neurological as it was like the messages I was sending my body wasnt being picked up at all, I couldnt even move slightly. I'd be laying in bed, completley helpless, looking down at my hand, trying so very hard to move my fingers or even just one finger and they wouldnt work at all, nothing would move. All this is one of the reasons why I believe Im at high risk of death if I crash again down to that. I had feeling in my fingers but like no response happening in them to my brain.
It wasnt a case of them being numb or in pain. With these episodes which could last a long time (by this I mean compared to paralyses of a sleep paralyses state), there was nothing at all I could do. I'd have to just wait to come good again, whenever that was going to be. Fortunately the bouts I had of it only lasted a few hours at the most. It was like having to wait for a worst ME crash to be over (thou a lot of the time I was comatose so didnt even have awareness I couldnt move). I was only being conscious for 20-30mins some days. (I was so close to dying from ME). This kind of paralyses was not due to me being half asleep.
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To the subject sleep paralyses thou, that is different again to what I'd call ME paralyses and sleep paralyses is COMMON among the normal populaton. I teach lucid dreaming (LD) and astral projection (OBE) to people online and it is basically the norm in those fields to happen to people. It happens when someone is caught between a sleep and a wake state, in the transitation state between.. the body has gone to sleep but the mind still has its waking consciousness, so is to do with brain states rather then a neurological disease thing. This is a natural physiological thing which is supposed to paralyse you while you sleep, otherwise you'd be acting out physically all your dreams. This state keeps you safe while you are dreaming, its completely natural.
If someone isnt aware of what sleep paralyses is and doesnt realise that they are expereincing a state their body is in each night but just awarely during transitioning states, yes it is then scary to them but to many of us who use that state for what we do eg those which do OBE and LD, its a state we can be aiming for.
Thing is with typical sleep paralyses, you are not going to be left in that state, it breaks as soon as you leave the transition state. It can be broken too if someone doesnt want to wait it out, with MUCH EFFORT to do so (you may need to put ALL your effort into it) by focusing on either a single toe or a single finger and keep trying to wiggle it till you break the state. (focusing on your body or doing something like getting out of bed, will not break this state if deeply in it) you need a small body part to try to move due to the effort it will take to move it.
It wouldnt surprise me at all if ME people get stuck in sleep paralyses transition states more then the normal population due to the fact many of us are tired (or sleepy exhausted) and hence those of us who have the illness severe are often going to sleep and waking up more times then most people do, so more opportunties to experience and get stuck in such states. We often have a lot more trouble waking up then ordinary people do (or falling asleep due to pain or whatever) so that too would increase chances of the sleep paralyses state being experienced.
Note.. with this kind of paralyses, halluncinations can be happening too.
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Itches are very difficult to ignore, so I would eventually decide to scratch it. It would take a lot of effort and mental focus to get my arm and hand to move and scratch the itch. It seemed it was as much my brain not wanting to tell my body to move as my body not wanting to move.
I dont know if its the same as what Ive experienced where I experience something which I'll describe as a type of exhaustion in which you really really want to do something but one is so exhausted that one doesnt, .. its a brain thing to me. LIke a lack of motivation but far more then that as its exhaustion on a mental level. The mental effort of doing something overrides ones will to do it.
I once peed myself in such a situation, cause I couldnt bring myself to get up and go to the loo, I really wanted to, but I couldnt bring myself to do it..due to the "mental" well I had physical too, but this was mental exhaustion which was like the straw which broke the camels back and caused me not to do what I wanted to do. I couldnt will myself to do it. I was so much effort mentally to get myself to the loo that I just peed where I was and stayed in the wet clothes due to my exhaustion. (till I was recovered from my crash enough to be able to mentally get myself together and get up and fix things). I could of moved if I had the willpower too but couldnt get it.
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Anyway... I just want to say I think all those three things above are different with different causes coming in for each of them. Same goes with feeling paralysed due to weakness. I can say the paralyses Ive had in the past was not caused by weakness (thou I was very weak at the time). Ive had weakness were I struggle to move too but that is completely different again and not what I'd call a true paralyses state which can happen in ME..
These issues should all be separately defined and each individually studied (except for the sleep paralyses thing as that is completely understable in our situations and even healthies get it, I dont think that would lead to any answers except shows we are going in and out of sleep states often etc).