What constitutes a full sentence in Japanese?

Question

In the three languages I know somewhat well, it's pretty easy to split a long sentence into shorter ones, which is a a way to avoid tedious flash cards. In Japanese, however, I find that I am not yet at a level where I can intuitively tell if my splits result in what would be considered complete sentences, probably because of the tendency in Japanese to leave out the subject. Note that the shortening is to learn vocabulary rather than grammar, so if a grammar point disappears it's not a problem unless it renders the sentence faulty in some way.

Let's take one of the first sentences in Botchan as an example:

小学校に居る時分学校の二階から飛び降りて一週間ほど腰を抜かした事がある。

This is definitely too long to be a good flash card sentence. Could I split this into:

1. 小学校に居る時分学校の二階から飛び降りる。
   (or the shorter 学校の二階から飛び降りる。?)
2. 一週間ほど腰を抜かした事がある。
   (perhaps even 一週間ほど腰を抜かした。?)

The English translation could be split (and slightly altered) into two complete sentences:

I once jumped from the second floor of my elementary school and was laid up for a week with a dislocated hip.

1. I once jumped from the second floor of my elementary school.

2. I was laid up for a week with a dislocated hip.

Answer 1

I would parse it as

[[[小学校に居る時分学校の二階から飛び降りて][一週間ほど腰を抜かした]]事がある]。

In other words, 腰を抜かした is a main verb, 飛び降りた is another main verb, and the two-part event is reported with 事がある.

So I would remove 事がある from both, or add it to both.