I used to have very similar symptoms, and actually wound up spending the night in an emergency room being monitored for a heart attack. Eventual diagnosis was a very severe gas attack. As others have mentioned, you could be reacting to something in your diet, and it could also be low stomach acid. Just because you've always eaten X, it doesn't mean you can still eat X. Your food really can turn on you. But you're going to have to do some experimenting, and be warned - it is a moving target.
The most common food sensitivities are to wheat and milk. Start by eliminating those. If either/both of them are triggering you, you will feel relief within a couple weeks. For me, I have self-diagnosed as having Irritable Bowel Syndrome, and I eventually got better by following a Low FODMAP diet. For several years, I avoided wheat and most milk products, among other triggers. Whatever was going on, it has finally mostly resolved, and I can now eat real bread and ice cream again. Although I am still careful, and I especially avoid eating later in the evening. And I also pay a lot more attention to getting enough fiber.
Although medications like Pepcid or Prilosec can afford immediate relief, you should not take them indefinitely. Too many doctors will put you these meds and just tell you to keep taking them. You actually don't want to reduce your stomach acid over the long term. Instead, you need to figure out what is causing the problem and fix it, and most likely it is something you are eating.
When it was really bad, I found that sleeping in a Zero-Gravity type chair worked wonders.
