There are many different causes of fainting
. The fact that you felt cold and clammy and hot spots in front of your eyes suggest that the most likely cause of the fainting in your case was a vaso vagal reaction, which occurs when the blood suddenly pools in the feet. This can occur with prolonged standing (not sure how long you were standing in line, for example), with stress, and with dehydration.
However, it is impossible to rule out a more serious cause of fainting based solely on this history. Other more serious causes of fainting would include a problem with your heart rhythm or other types of heart disease. Therefore, it is generally advisable to schedule a follow up with your primary care doctor
after any episode like this. They can examine you from head to toe and determine whether any additional testing is needed. If the exam is totally normal, then they might concur that this was just a vaso vagal episode and that no additional testing is needed.
In the meantime, if you experience any palpitations, chest pain, shortness of breath, or recurrent fainting, go right to the emergency room for evaluation, and don't wait to get in to see your doctor for an office visit.