Thanks for the query to ATD for an opinion,
Anal sex is a form of unnatural sex and yes, it is true that in some women due to increased stretching or poor lubrication or poor pain due to stretch tolerance while insertion, there may occur vasovagal syncope due to stimulation of vagus nerve which can cause decreased heart rate and drop in the blood pressure, leading to dizziness and fainting attacks. So It is not advisable though but if practiced one should keep vast-vagal syncope in mind , though the incidence is 5-10%.
I hope i have answered your query in detail,
Wishing you good health and safe natural sex,
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.