Aged 77yrs, male, overweight, being treated for hypertension (high BP)..attacks of "unsteadiness".........the first thing that comes to mind is that both amlodopine and atenelol are for lowering your BP and one wonders if it is being lowered too much.......so a BP check is the first port of call.
These attacks that you describe do not have any of the characteristics of vertigo, so that rules out many other conditions.
Your problem does seem to involve your cardiovascular system one way or another and a visit to your doctor would be the obvious next move.