I'm a junior doctor but this is an internet forum so ...
A heart attack occurs when blood supply to parts of your heart muscle is cut off, usually by narrowed arteries. One of the best (easiest) ways of measuring whether or not any damage has occurred is with blood tests because there are certain enzymes (e.g. Troponin or CK-MB) that are only found in heart muscle. If you find these enzymes in normal blood it indicates that they've leaked out - essentially from dead muscle tissue.
However there are other conditions, e.g. infection or inflammation, that can make the muscle cells leak. Often without any significant damage having occurred. If your sharp pains were affected by your body position it could be a something like 'pericarditis' (which also causes changes on the ECG).
They key thing for you as a 29 year old is that you are very unlikely to have narrowed arteries. (Unless you have a very bad family history of heart problems).
The heart attack risk from exercise arises when you need more blood supply to get your heart muscle pumping more, and narrowings limit the maximum flow rate. If your arteries aren't narrowed there shouldn't be any increased risk from exercise.
You really need to discuss this with an expert, if you are labelled as having an MI at 29, it will seriously affect things like insurance, mortgage, driving, flying etc for the rest of your life, and it is very unlikely. I certainly wouldn't accept that label myself without evidence of narrowed arteries - (ischaemic disease).
On the other hand, if you have had an MI, then knowing earlier will let you do more to avoid problems in the future.
Anyway, hope you're feeling better, take it easy.