Occasional 'catches' of breath like all air has gone from my chest, lasts 5 secs & with dizziness. light heart pain. flutters too. ecg, bloods fine.

Tachycardia: It sounds like you may be having short bursts of tachycardia (likely SVT in view of your age). A heart rate of 180-220 is common, may only last a few seconds, and would produce all the symptoms you describe. Ask your doctor for a 30 day event monitor exam to nail the diagnosis. It's easily treatable. Meanwhile, avoid nicotine and caffeine.