For your own peace of mind, it would be wise to see a cardiologist and put this all behind you so that you can dismiss it and go on with your life.
I started having palpitations when I was 17 and had them all through my life until I had a pacemaker implanted at age 70. It turned out that my particular "palpitations" were atrial fibrillation.
It's an irregular beating of the atrium, and when it kicks back into normal rhythm, it kind of changes gears, so to speak. That's when I felt dizzy.
I hope you will see tha cardiologist soon as the anxiety is just too hard to deal with.
I am so sorry that you are going through all the anxiety of fear of the palps.
Yes, they can certainly be due to stress, even though your husband died 4 years ago, it is still stressful, and it can still have a major effect on your nervous system. Also, worrying about you son and dying is more than likely contributing causes.
I have these horrid things, and I can sure relate to your fears, they are very real, I live in fear daily..
The weakness and dizziness are anxiety as well. When folks get a rush of adrenalin, whether for a happy reason or sad, they release the fight or flight hormones, and these will give you the rubbery legs and vertigo and certainly cause you to be tired.
Don't worry, your heart will not stop because of these. For peace of mind, it might not hurt to tell your doctor, and maybe he will do an Echocardiogram to rule out any structural problems and some other tests. Given your age, however, I am sure the tests will all come back just fine. :)