英语造句:fall belind和fall over

fall behind 1. 落后，跟不上。
Some students become depressed because they fall behind.
一些学生因为落后而变得抑郁（消沉）。

fall over: 摔倒。

If I walk too quick I will fall over.
如果我走得太快，我会摔倒。

fall over + sth.
for example:
I paddled too fast that I fell over my bike.

我楼上的解释还是不错的。不过第二个造句动词后加副词，所以是“If I walk too quickly I will fall over”