I have started to wake up to sweat and heart racing. wakes me up at 4am. happens during ovulation week and sometime during my menses. i'm 42.

Many things.: It could be any of many things. From mitral valve prolapse to aberrant electrical heart system to cardiomyopahty. It is not normal and you should go to see a dr. For full evaluation.

More info: Do the palpitations awaken you or do you awaken with a startle which causes the heart to race? How fast is your pulse when you note the palpitations? How long do they last? Do you also get palpitations on other occasions. A pulse rate of 120 to 150 has more significance than one of 90, for example. A startle reaction may last a minute or 2 as opposed to significant tachycardia. Consult your md.