Hello Hasy, The expression is not odd; the sentence as you wrote is rather wrongly formulated. The correct sentence would be: " I 'am afraid I cannot sleep at night". It means having feelings of worry, concern and insecurity about the fact that he/she cannot sleep at night. The expression " I am afraid ------" is a widely used idiom as well and means " I believe ,regrettably ------" For example : A: Please try to come to the party tonight. B: I am afraid I can't make it tonight,but I will try my best. It is sort of an apology for not being able to attend the party and to accept the invitation. This meaning is not the one conveyed in the sentence you mentioned though . Again you could use the expression " i am afraid of" but in that case the sentence need to be rephrased to be grammatically correct. You could say: " I am afraid of not being able to sleep at night".

The sentence is odd to the native English speakers. Remove the "of" from the sentence, "I am afraid, I cannot sleep at night"