Are you doing it right? I should explain a guide here.
After dropping to the wooden plank, make your way to the rope. Be careful not to miss or fall at an angle where you'll hop off and land somewhere down in the platinum mines and die. Slowly (or fast, as long as you don't move left or right while walking) make your way to the next plank. Now, if you have some potions, use them, and if not, wait to get about 90% of your health left (or 100% if it's really low) and hop down to the wooden platform below. It helps me if I land on one of the guard rails off to the side of the platform, since they're a bit closer to where you're jumping from. If you have about 98/100 health as your max, you may wish to do this, it can save you. =P