What does 'losing patience' mean?

[Rich7]

Test No. incompl/inter-76 "Christmas Postman (3)", question 2

After about two hours of this my internal battery started to get low and I found myself losing ..........

(a) patients
(b) patents
(c) patters
(d) patience

Test No. incompl/inter-76 "Christmas Postman (3)", answer 2

After about two hours of this my internal battery started to get low and I found myself losing patience.

Correct answer: (d) patience

Your answer was: correct
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please explain the whole meaning of this sentence for I do not get the essence?

[Alan]

This means: After about two hours I was beginning to feel weak and tired and I was starting to feel as if I didn't want to do any more because I didn't have any more patience left.
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English as a Second Language
You can read my ESL story A day in the life of a parliamentary candidate