High:
OP sounds sketchy.
However, there is no exact point of immobility.
Some get to that point quicker than others for a variety of reasons-pain, lack of musculature or some other impediment, like being too heavy.
500 lbs can render someone 5 foot tall immobile, whereas it won't for someone 5'11".
Get a membership to a gym that has a pool and use it for low-impact workouts. Dump your man if he's not on board.
I feel like this is worth discussing even if the op is fake.
There are a lot of factors, but one of them is also how desperately you want to remain mobile, and what you consider immobile. For instance, vanillahippo is over 800 lbs, but also 6'1 or 2 and literally big boned. She's effectively house bound, but can stand and walk on her own and get around her apartment and use the bathroom (I don't know what her set up is but it's not a bedpan.)
Echo is comically short, so she looks even more massive than vanillahippo while weighing 100lbs less, but because most of the weight is in her legs and ass, she can still stand and ever so slowly shuffle to a toilet. Technically she's not immobile, but she's almost always in bed now and getting to the bathroom is exhausting...so she's right on the line, to the point that "mobile" wouldn't be accurate.
Jesstastic has the body of a Barbie doll with the gut of a 450 lb pregnant woman. She's already suffering aches and pains and 500 lbs will probably keep her in bed.
All that being said, unless you suddenly suffer an injury or an extreme illness, immobility isn't going to sneak up on you if you're trying to stay mobile. You'll know when it's getting close and it will be a long time coming. The only way you'll be surprised is if you give up. That's how it happens. Either because of depression or pain or enabling, you just decide to stay in bed one day, and someone caring for you makes it possible for you to stay there. And a day turns into weeks. Months. One day you decide you want to get up...but your legs are too week and you fall. So you rest, before giving it another try...and never do.
