Repeated episodes noted over few weeks of same pattern over bowel movement noted by you are not common. It is not the presentation due to vagal hypertone as suggested to you where partial loss of consciousness- syncope is a feature. This , a rare presentation due to over- stimulation of some specific cells called Mast cells by hard stool passage in bowel forcing them to release an active hormone serotonin into blood stream with dramatic manifestations experienced by you for some time.
To make sure, it is Mastocytosis only responsible, YOU may undergo a rectal biopsy and endocrinologist consult. A suitable anti serotonin drug prescribed will help you in any case.

Hello!
Constipation is a common concern in elderly people, do not worry. To relieve the constipation and prevent further episodes of it, I would recommend that you:
- Eat a lot of fiber containing foods, such as vegetables, beans, fruits, oat etc. You can take fiber supplements as well, such as methylcellulose.
- Drink plenty of water and fluids during the day.
- Reduce the daily consumption of coffee, tea and alcohol.
- Do regular daily exercise, at least 30 minutes walk a day, may help to increase bowel movements.
- Use stimulant laxatives (such as Senna tea) or osmotic laxatives (such as sorbitol, magnesium salts, lactulose etc.).
* Please use the laxatives according to the given instructions by your pharmacist or doctor.
*I want to inform you that, if none of the above recommendations is helpful, or if constipation persists for longer time and especially if it is associated with other symptoms such are blood in stool and/or weight loss, please consult a gastroenterologist for an evaluation of your large intestine (colon).
I wish you good health and thank you for using healthcare magic! I hope my recommendations will be helpful to you.
All the best,
Dr. G. Topi