Answer:
This is a sentence.
Step-by-step explanation:
There are many differences that indicate if something is whether a sentence or a fragment.
For example, fragments don't contain a finished thought, on the other hand, sentences do. Fragments don't contain a subject, while a sentence must have one. The same is with verbs and fragments, they may contain a verb, and a sentence always contains it.
Fragments don't have independent clauses and sentence always have them, at least one.
We came to conclusion that this is a sentence because the thought is finished and we can see that someone is something ( Patrick is afraid ) and we also know WHY he was afraid of something. In this sentence, we have a visible independent clause.