Those who ate the poison berries and vomited lived while those that ate them and did not vomit died. Vomiting can be very useful. Almost everybody at some time but some more often that others. You are most sensitive at about 12 years of age with declining susceptibility as you get older. Asians are generally more prone to seasickness.
Women become ill more frequently especially when pregnant or near menstruation.
You are at greater risk if you are fatigued, anxious, sleep-deprived and if you consume alcohol or certain medications. Don't drink alcohol when traveling. If you are taking opiate pain medications or aminophylline ask your doctor if there is an alternative while traveling. When you use them, try to take or apply them before activities which may make you ill. As much as you can, relax and get enough sleep.