Well, that depends on the form in which the phrase is used on the sentence. The first example: "Her attention suffocated him, as if it were a snake", The phrase "as if it were" can be translated as: " como si esta fuera" o " como si esta fuese". On the second sentence: " He told a joke, but nobody laughed. He felt as if he were naked, in a room full of people with cameras." ; The phrase "as if it were" can be translated as: "como si estuviera". Both of these phrases could be correct, but that depends on the form and the meaning of the sentence.