The correct answer is option 4 i.e. Mr. X fell down and was losing consciousnessLet's look at the following points-The tense used in the first clause is the present progressive(continuous) tense.Whereas the second clause contains simple past tense i.e. "Mr X fell down" and in past continuous tense i.e. 'Mr. X fell down and was losing consciousness'.Now, look at the following points-When the simple past tense and the past continuous tense are used together in a sentence, it shows that the action referred to by the simple past tense takes place somewhere in the middle of the past continuous action.These tenses are often used to show an action interrupting another action.For e.g.- I was working when someone knocked at the door.Explanation Losing consciousness is an instantaneous action which cannot go on for a period of time. There is a definite 'point' where the person falls unconscious. Hence, we may conclude that in this sentence, it was an effect of Mr. X's falling down and would take the simple past tense. ?Correct Sentence- While trying to collect an envelope from under the table, Mr. X fell down and lost consciousness.