Thanks for the query to H.C.M. Forum.
It may be due to stress
, bowel movement are common features in tension and hyper acidity.
However tension and stress also develops hyper acidity , so most probable cause is stress and anxiety
If age ( you have not mentioned in query) is around 50 years may be due to hormonal
Rest and bland diet will help.
If symptoms reoccurs than consult a physician.
Hope I have answered your question.
If further any question I will help.