Sorry for a long rambling post, I'm having trouble editing my thoughts and I wrote this in two bits, hopefully it still makes sense!
As to whether it was an overnight thing. For me, yes and no. I'd been okayish in health as a kid, I didn't have perfect health, prone to infections, asthma etc. But definitely didn't have ME as I understand it now, till I caught something which I had no idea what it was when was about seven and till I started periods aged nine, when my health really started going down hill, it turned out I had endometriosis and I was really ill with that from the off. But after those two things I went from being a healthy enough kid in general terms, who'd walk for miles and miles and miles okay etc. Because we didn't have a car and used to walk for recreation when I was little, to being very unwell pretty much all the time. If there was anything going round I'd catch it and couldn't seem to get rid of it for weeks, and often would just spend days in bed completely worn out sleeping pretty much all day for days on end. I wound up being home educated because school just became too much in all ways. After that I had been steadily declining over a past few months but was able to walk etc. It would, for example take me a solid week to recover walking to the GP on a flat, easy ten minute walk, because i'd just be so ill and exhausted in a way none of us understood, but I could do it even though I'd pay for it.
Then I had to have surgery under GA for endometriosis when I was thirteen and it was suddenly a really steep, rapid decline after that, but I could just about still walk etc. Like to the GP as I say above. It it would make me ill for a week, or be able to walk downstairs but then would be restricted to the sofa all day completely lacking any energy at all. Then one weekend, almost exactly a month after the operation, I was able to walk into the garden and sit in the swing seat but it took me all day to be able to walk back, the next day I could just about crawl from my bed to the toilet, the next day I couldn't stand at all unaided, was having trouble staying conscious, talking when I was etc. Etc. I had very severe ME at that point and for a good few years after and it was that dramatic decline that lead to me being diagnosed by a consultant rheumatologist after my GP got me taken into hospital as an inpatient. He'd already suspected ME and was in the process of referring me to a paediatrician to confirm it, but this total collapse sped everything up as I got taken into hospital for a spell.
In hindsight I was ill for a very, very long time before this collapse, with which I now recognise as ME, again I think from the age of about seven. but because no one knew it or understood what was happening, I think I wound up bed bound because I just over exerted for years and years till I had that operation and I think my body kind of went 'woah, that's enough!'. I've now improved to having severe ME rather than very severe, but that seems to be what I'm stuck at and it does make me think that over exertion for all those years did some damage that my body can't heal, I've never been past being severe since then. I've been housebound, except for sporadic outings in the year, which make me really ill but I sometimes have to do for the sake of sanity or to see dentist, optician etc. I've been totally reliant on a wheelchair, inside and outside home. And pretty much entirely bed bound. Even sitting in an armchair is exhausting to me, I really struggle to maintain posture etc. But I've managed to get a specialist chair that helps, meaning that I'm not technically bedbound because I'm not stuck in bed anymore, but I would be without this chair if you see what I mean.
I think Sue is totally correct about choices, they aren't always easy to make! I very rarely leave my bedroom because typically speaking I'm just not well enough and to me it never seems like a sensible use of energy give what little I have of it. I'd rather use the same amount of energy in my bank to read something as in really read it and actually take in what I've read!, or watch something, or play a game,for a short time, or chat on the phone to my sister, or talk to people on here, or store it to go out somewhere every now and again, or before I had to take a break do a bit of study etc. etc. it just never seems like a good use of energy to me to use energy to go downstairs just to say I have done, if that makes sense! If I leave my room it's usually for a specific outing for which I've stored up a ton of energy as best I can. So maybe I should say I'm 'bedroom bound'. I choose to stay bedroom bound because I can actually have the energy to be able to engage in some sort of activity while in my bedroom, rather than leaving my bedroom and that being the activity I do. It's a case of either/ or for me, I can't have both, I've tried.
It's deeply frustrating when you want, and indeed need, to do so many things in life to be so restricted but I am very, very aware when I over do things just how easily I could slip back to being very severe. I really got scared at the end of last, start of this year, I could feel myself declining in a way that was scary because I had to over exert, which was unavoidable. Honestly it terrified me. I'm still very delicate now, and still feel at risk of it at times, but I'm hoping careful pacing will help me to improve. I'm not perfect at pacing, I get very frustrated with how restricted I am I get very tempted to prove myself wrong about my limits and 'try harder' despite knowing that's destructive. I get tempted to just 'push through it' despite knowing better and despite feeling so delicate. It's tough! I think people on the outside don't realise just how tough it is to stick to disciplining yourself to stick to your limits. But it's true that if you pace you can actually achieve more than if you push yourself on and tell yourself too just push through it, just get it done etc. This is something I'm definitely finding. So I'm hoping these wobbles where I'm tempted to 'push through' something, rather than break something down into chunks I can cope with, and where I don't pace properly happen less and less. I'm also having tests done by Dr Myhill so I'm hoping that helps too.
So My advice would be to pace, pace, pace! And wherever possible get some help and support. Will be thinking about you, Strawberry, I really hope it all works out.