what do people mean when they can't even stand?

I noticed a lot of people stated that they are bed bound, but what symptoms caused this? I had extreme chest tightness and high heart rate as well as this sick feeling, but wondering what others have felt and if mine is similar.

I am someone who can't stand for long. I can't even sit for long. You just can't either balance or have to move around a lot. I just find I tired so easily and coordination is so off that sitting or standing takes so much energy you just have to lie down. I have been like this for 3 years now. But this morning I was able to stand for quite a great length of time.

I was not able to stand for some months due to severe numbness/tingling in legs.