I think you have too much acid in your tummy, it bubbles up, and this can irritate your throat and cause the esophagus to spasm if it goes on long enough. Spasms can come and go, caused by sometimes if you're stressed out, sometimes if the food you eat is too hot or cold, various triggers, with acid bubbling up being the main one. So, your last doc's meds are ideal for you, because the Galviscon soaks up acid, the Donnatal eases digestive spasming, and the Valium is to prevent too much stress and is also relaxing.
The thing about spasms and pain is, when a muscle anywhere in the body seizes up to some degree, it REALLY hurts. And the thing about a muscle spasms is once they have a tendency to do that, sometimes it's hard to make it stop as a kind of body habit, and they will repeat almost at the drop of a hat. I get spasms in my back where I hurt it in a car accident, for years and years it's done that, and does it ever bring me down, and I mean, I don't even have to be doing anything diff and they'll set off. So, keeping one's self relaxed is key to any muscle spasm thing. And then the source, it has to be treated, which is the acid in your tummy. So, those medicines are a good combination.
Sometimes medications you take for other conditions can cause an acidic stomach and the spasming, so getting enough water to drink helps. You can look on the internet for foods that are naturally alkaline, maybe more of those will help offset acidic foods that you should have. The less your esophageal muscles spasm, the less they will start up again. Honey, by the way, is quite soothing to the throat, maybe you could mix some up with a half-glass of milk, and drink it sometimes as a snack type thing. Exercise helps keep a person in a relaxed state. And if you are energetic and tend to do too many things all at once, just slow down, cut back on some stuff that isn't important, take time to enjoy life. I hope some of my thoughts help you out.