There are many unpleasant ways of waking up. You may awake to find that your bed has been set adrift in a river full of piranhas or painted a tasteless color. You may awake to find that your family has perished in a fire or eaten all the scrambled eggs. And you may awake to find yourself in a morgue, twitching slightly because someone else committed suicide for you, although that should really be your decision, don't'cha think!
Mr. Hyde sat up. He was immediately greeted by the stench of decaying flesh and cheap perfume, the general impression being that of having been laid to rest in a room full of zombie prostitutes. Given Hyde's favorite method of entertainment, zombie prostitutes were not a prospect he found entirely to his liking. So he left (1).
Hattie Pearson prided herself on three things: Her unusually gentlemanly clientele, her good manners (she was not nearly as forward as many of her coworkers), and her delicate, rosy complexion. Ah, yes, she was a regular lovely lady.
So needless to say, being called "malevolent, busty hell-wench" by an alarmed, cane-wielding stranger did not agree with her. So she pushed him in the Thames.
There are not many pleasant ways of being dumped in a river.
(1) Yes. Mr. Hyde just up and walked out of a probably locked morgue. How? Because he's Edward freaking Hyde. That's how.