Could I say sentences like : "I fear skydiving" or "I fear being enclosed in small spaces" or are such sentences wrong? Would I have to use "scared of skydiving/being enclosed etc" or do I need to add the preposition "of" to fear? "Fear of skydiving"? (so use fear as a noun and not a verb)
"I fear skydiving." is a complete and correct sentence. In this sentence, fear is the verb.
"fear of skydiving" is a noun phrase, not a complete sentence. Fear is a noun in this phrase. You could say "I have a fear of skydiving"
In the phrase "scared of skydiving", the word "scared" is an adjective. You could also use "afraid of skydiving"
Using "I fear skydiving" instead of "I'm scared of skydiving" is a little more formal, and less common, but both are correct.
The reason for all these synonyms is the multiple sources of English. "fear" is Anglo-saxon, as is "fright" but from a different source, "afraid" is Anglo-french, and "scared" is from Old Norse. The stronger "terrify" is from Latin.