The problem could be gastritis and if the potato was spoilt then the response is aggravated. Potato has more of serotonin content in it and is a mood stimulant. Since you have cooked it well, then bacterial infection is less likely and could be mild as well. Now for vomiting I would suggest you to take an antiemetic after a prescription. It is not dangerous and once the food that is infected is cleared, you should be fine.