There are many issues that arise. The body is not designed for high pressures.
As an example, as you go lower, you have to breathe air which has a smaller and smaller concentrations of oxygen. This is because if the partial pressure of oxygen rises too high (1.4-1.6atm), it becomes toxic and kills you.
There's nitrogen narcosis. Nitrogen has a narcotic like effect on people at depth (20-30m, depending on the individual), and deep see diving is not a healthy place to suffer narcotic effects.
Going below 150m with helium in your breathing mixture comes with the risk of High Pressure Nervous Syndrome, which can cause all sorts of problems. In fact, many commercial divers will breathe trimix, a mixture of oxygen, helium, and nitrogen. They introduce the nitrogen, and the risks of nitrogen narcosis, to decrease the partial pressures of the helium to offset HPNS. These mixes are often adjusted on the fly, depending on your particular depth at that time.
Around 2-4km deep, we believe we will run into issues with helium narcosis. Helium is considered to be the least narcotic gas known, and models suggest it becomes fatal at those depths. At this time, nobody knows if there's a way past that boundary or not.
The human body was not designed to survive the pressures 100km down. It's chemical engines are simply being run outside of their specifications at that point.
Edit: All of this was based on the idea that the hole was in water. If the hole was in air, obviously the pressures accumulate much slower. This calculator suggests that at 100km, we would experience an air pressure of 500atm. That's roughly equivalent to 5km depths of water. So if that calculator is correct, the bottom of the hole will still be just outside of the limits of the human body's susceptibility to helium narcosis.