meaning

i dont understand these passages from The Haunted House by Charles Dickens. can anyone please explain them in simple english:

I had got into the train at midnight, and had fallen asleep, and had woke up and had sat looking out of window at the brilliant Northern Lights in the sky, and had fallen asleep again, and had woke up again to find the night gone, with the usual discontented conviction on me that I hadn’t been to sleep at all;— upon which question, in the first imbecility of that condition, I am ashamed to believe that I would have done wager by battle with the man who sat opposite me.

At first I was alarmed, for an Express lunatic and no communication with the guard, is a serious position. The thought came to my relief that the gentleman might be what is popularly called a Rapper: one of a sect for (some of) whom I have the highest respect, but whom I don’t believe in.