mrcem2-0659

A 45-year-old man presents with severe nausea and recurrent vomiting. The vomiting episodes occur every few weeks and are accompanied by colicky abdominal pain. However, his bowel movements are normal. He reports that the only relief he gets during these episodes is by taking hot baths. He has no significant medical history but admits to being a heavy and regular cannabis user. A complete set of blood tests and an abdominal X-ray are performed, both of which come back normal.
What is the most probable diagnosis in this case?