What could be wrong?

If he can't feel his legs he may have a neurological problem. He also may have had a stroke. He needs to see a doctor immediately.
Take care,
Carol

Carol is 100% right. He should see a Dr. right away. Any change in status should prompt a Dr.'s visit.

I took him to the E.R they did Blood work , a Chest Xray,& EKG everything came back negative

Did they do a CT scan on his head to check for stroke? Are there any other symptoms? Maybe it is a problem with his eyes? Or if he gets dizzy, that can be caused by dehydration. Does he drink enough fluids?

My husband fell often. I'm not sure if he could no longer feel his legs, but he could definitely no longer control them. His neurologist and sleep psychiatrist together theorized that he might be having narcoleptic-type episodes. Treating hime for narcolepsy solved the problem!

I just mention this to point out there are many possibilities to consider. I agree with all the others that this needs medical attention, and not through ER.

This could be cardiac as well. And highly treatable if it is some kind of arrhthymia. Medical attention ASAP.

ER might not have found it, a more extensive exam and a Holter monitor for more extended cardiac monitoring might. Jeanne is right.

He maybe experiencing a drop in blood pressure when he stands up. This could be dehydration, but hey would have picked that up in ER. Sometimes when the heart is not profusing properly these episodes can occur. Aortic Stenosis, diagnosed by an echocardiogram, is one possibility. Have him sit on edge of bed for a while before he stands.