My tip is when you see "unless" on the right side of the sentence, instead of translating as "if not", take contrapositive of the condition and it will be faster. Imagine the conditional arrow => strike through the "unless"! I will diagram the sentence you use as an example: (MMI <--> ME) => MMI before ME

The diagram in plain English: If Major Meteor Impact causally link to Mass Extinctions, then Major Meteor Impact occured before Mass Extinction (or "mass extinction have followed major meteor impacts).

When mention "draining", how long into the session that you start to feel that way? Is that the 3rd and 4th passage? What you experience is probably brain fatique. Then you should do a marathon, which mean doing a drill with 5 or 6 passage in the row and don't check your accuracy and don't take a break in the middle. This drill will train your brain for endurance. You can work on accuracy separately. Try that drill once a day for a week to see if you feel less brain fatique. Also, you don't need to memorize all information, you need to know where the information located and come back to review it when you do the question.