What happens one January day in Regent's Park?

One January day in Regent's Park, Jekyll turns into Hyde naturally..... without drugs. He is losing control, and Hyde is taking control.

And at the very moment of that vain-glorious thought, a qualm came over me, a horrid nausea and the most deadly shuddering. These passed away, and left me faint; and then as in its turn the faintness subsided, I began to be aware of a change in the temper of my thoughts, a greater boldness, a contempt of danger, a solution of the bonds of obligation. I looked down; my clothes hung formlessly on my shrunken limbs; the hand that lay on my knee was corded and hairy. I was once more Edward Hyde. A moment before I had been safe of all men’s respect, wealthy, beloved — the cloth laying for me in the dining-room at home; and now I was the common quarry of mankind, hunted, houseless, a known murderer, thrall to the gallows.