What Causes Chest Tightness And Dizziness?

I am a 42 year old female, am not overweight, exercise regularly and am a non-smoker and drink within sensible limits. For the last few months I have been experiencing left sided chest tightness, it is not so painful that I need to rest, it is more a niggle and can last for 10 minutes at a time. It usually comes on when at rest and does not seem to be exacerbated by exertion. I feel the frequency of this has increased recently and is now occurring several times a day. I have also noticed an increase in dizziness when I stand with standing or sitting. I have always had low blood pressure but it is now taking more than a few seconds for this to resolve. I am reasonably fit but today when I was jogging I was aware that I started to feel dizzy and nauseous and had to finish my run earlier. The chest niggle was not present at the time but I did feel it about half an hour later. I am worried by all the symptoms and wonder if cardiac related, advice appreciated.