Is it indigestion?

Three times throughout the day today - once in the morning, then again in the afternoon, and again at night - I experienced the feeling of small bubbles(like gas) forming at the top of my stomach, right below my heart, and then my heart starting beating rapidly for almost 30 seconds each time. Could it be indigestion? Or anxiety? Or something more serious?

It could be any number of things - gas, acid reflux, anxiety, gallbladder issues. Doesn't sound normal and you might get it checked out by a doctor.

It could be all three, but it's probably anxiety.
If you continue to be concerned or bothered by it, please see your doctor.

It could be on of the three but the fact that your heart starting beating rapidly rules out the indigestion and leaves anxiety or tachycardia - or racing of the heart beat-- since it happened 3 times today, I really don't want to tell you to go to bed with this because if it happens while you are sleeping and leads to a heart attack, you won't know it--- so I have to tell you to get yourself to an ER do not drive-- it is very important that you do not drive because you can have this attack while driving and it can cause you to have an accident--- go to the er---they will put a heart monitor on you, do cardiac enzymes to see if you had or are having a heart attack, an EKG- to check the rhythm of your heart and see if there are any changes of a previous episode with your heart, and you will be there over night and tomorrow. They will have a cardiologist see you and they will most likely do a stress test before sending you home........good luck to you....call a cab.