IF A BLACK HOLE THE SIZE OF AN ATOM SUDDENLY APPEARED IN THE SAME ROOM WITH SOMEONE

You'd be torn apart. A black hole the size of even the smallest atom (around 0.03 nanometer radius) would have a mass of 3 times 10 to the 16th power kilogram. At a distance of around 3 meters, it would produce an acceleration of much more than 100,000 newtons per kilogram, or 10,000 times Earth's surface gravity. You'd be obliterated instantly. Even the tidal forces between opposite sides of your body would be enough to shred you cell by cell.