Hello from JustAnswer.
It is very possible that these episodes could be anxiety or panic attacks, even though they are not associated with any particular separate sensation of anxiety. However, since there is no direct test to prove an anxiety or panic attack, the diagnosis is made by an evaluation to exclude other possible causes of the symptoms or empiric treatment of anxiety/panic.
The most important condition to exclude is heart disease, as this would be the most serious condition that could cause these symptoms. So, it is very reassuring that a cardiac evaluation has already been done and found no significant disease.
Once heart disease has been excluded, then there are two options. Either the doctor could start a medicine for anxiety to see if the symptoms improve or further evaluation to exclude diseases of the lungs or GI tract can be done. Since your doctor has already expressed that these are due to anxiety/panic, it would be reasonable to use an anxiety medicine to see if the symptoms improve, such as an SSRI antidepressant.
Regardless of which approach is taken, you can be reassured that there is not a serious cause of these symptoms.
If I can provide any additional information, please let me know.