Hi Eva, as Giuseppe has said, your second sentence is not grammatically correct. The correct form should be "Sento di essere caduta in una trappola" (without "come"). That's because, the first sentence, "SENTO + COME + SE + FOSSI (SUBJUNCTIVE MOOD)", expresses a situation of analogy and hypotheses, more or less: "I'm feeling as i think i'd feel if I fell into a trap" (I'm feel like i'm trapped, but i'm not really trapped!). Indeed, the second sentence "SENTO + DI + ESSERE (INFINITIVE MOOD)" expresses a situation of certain perception, more or less: "I feel i'm trapped 'cause somehow i feel the trap around me".
I'm sorry if my explication is a bit confused or if my english is uncorrect! :D I hope you will understand anyway!