73 Years Old, Diagnosed With Cancer But Getting Frequent Dizzy Spells

she is a 73 year old woman who has been getting dizzy spells for awhile and they seem to be getting worse and more often i speak of my mother n law.she has just battled cancer and won.but doing so has taken alot out of her.for the past few months she has begun having her dizzy spells.she has done many test that have all come back with a clean bill of health.but with time they have gotten worse,and seem to happen every time she gets up,for any reason.she becomes very dizzy,shaking,and in the end not sure where she is doing or where she is.they dont last long but are becoming scarier,for all of us.