Examples

Boom. The speaker is talking about the act of falling. If "falling" were used as a verb here, we'd have a sentence like: "I'm falling head over heels." or "I keep falling down the stairs." See the difference?

If you want more proof, just replace "falling" with the first noun you can think of. Let's go with homework:

Homework is something I do way too often.

Well, excuse you.

We certainly aren't judging.

Here's an instance where an entire gerund phrase is being used: dancing with my underwear on my head. Replace this with absolutely any noun you can think of, and it'll make sense.

Ha. Gotcha.

This example does not contain a gerund. Here, "is running for office" is a predicate, and the verb phrase "is running" is in the present progressive tense. We put this here to show you that just because the present participle follows "is," that doesn't mean it's a gerund. Also, that the ol' replace-it-with-a-noun trick isn't always reliable.

Contrast with these examples:

My favorite pastime is running.
My lifelong goal is running for office.

Now those, dear Shmooper, are gerunds.