Question about a passage

The question I have was brought up by this passage on page 270, "I should have been chary of discussing my guardian too freely, even with her, but I should have gone on with the subject so far as to describe the dinner in Gerrard Street, if she had not then come into a sudden glare of gas. It seemed, while it lasted, to be all alight and alive with that inexplicable feeling I had had before; and when we were out of it, i was as much dazed for a few moments as if i had been in lightning." Firstly, I don't understand what is going on, it seems as though she farted but that seems against her character and Pip's reaction "as if i had been in lightning" doesn't seem like a reaction to a fart. More importantly though I don't understand if this was supposed to have relevance on their relationship, Pip being caught before he said too much of his guardian and realizing how he is unable to control himself in front of her. It seems very out of place.