I sure hope I don't fall down.
well bacically u write fall in the sentence
Beware that you do not fall a prey to the highwaymen who stalk these roads.
Example sentence - The small child was unharmed after a fall from the staircase.
May has two meanings, it suggest that you have permission to fall or it suggests that the possibility exists that you will fall. In the latter sense you can use "may"
I wear a jacket in the fall time.
That man grappled on to that cliff and he was about to fall off.
a big scud of rain will fall
storms happen a lot in the fall
i need to tighten my belt or my pants will fall.
That detestable warlord Khan must fall!
i will see you in the fall if i see you at all.
The ocean was murkier in the fall then it was last spring