If this happened to you , you need to call us right away to repair it. The shims in the stringers which held your treads and risers in place have broken and the entire step has collapsed. This is something that can be avoided with a quick checkup.
Things to look for so this doesn't happen to you .
#1 . Very squeaky step.
#2 . A lot of movement in the step while walking on it.
#3. Gaps between the stringer and the treads like the picture shown above. ^^^^.
#4. Gaps between the riser and the treads (below the nosing)
#5. Cracks across the entire tread.