Tosefta su Salmi 130:78

A person should not stand on top of a bed, and not on top of a chair, and not on top of a bench, and not on top of [any] high place and pray [Shmoneh Esreh], because there are no high places in front of God, as it is said, “From the depth I called out to You Hashem.” (Psalms 130:1) [However,] if he was an elderly person or sick then it is permitted [to pray Shmoneh Esreh on top of a high place]