Here's the official warning:

CAUTION: YOU WILL BE TRAVELING UP TO AN ELEVATION OF 14,110 FT. SOME PEOPLE MAY EXPERIENCE ALTITUDE SICKNESS WHICH MAY INCLUDE SYMPTOMS OF DIZZINESS, NAUSEA AND HEADACHES. IN ADDITION, IF YOU ARE PREGNANT OR HAVE CARDIAC OR RESPIRATORY PROBLEMS, IT IS NOT ADVISED THAT YOU MAKE THE ASCENT WITHOUT FIRST CONSULTING YOUR PHYSICIAN.

Note: The vast majority of passengers on the M&PP Ry. have no problems at all, but some people do experience discomfort. To minimize your chances of suffering from the above symptoms, it is advised that you get plenty of sleep the night before by avoiding sex and alcoholic beverages, and drink plenty of water on the day of your trip. If you are unsure, consult a doctor!

Follow the advice, SG!