Just as death in a dream can represent moving to a new stage in life, collapsing in a dream can represent the ending of something and the start of something new.
In general, if you collapse in a dream, or if you see someone else collapse in a dream, you are entering a stage in your life in which the thing that caused you or that person to collapse no longer plays an important role.
For example, if you dream that you collapse from sorrow, you are entering a stage of life in which you will be happier; if you collapse from physical weakness, you are entering a healthier stage of life.
Dreaming that a building collapses can mean that you don’t trust the foundations on which an idea, project or relationship are based.