Hi MissB, I have been having similar problems. I started a new exercise program almost 3 weeks ago. In the past week I am feeling really tired, and cardio which used to feel easy (30 min on the elliptical machine) is now causing heart palpitations. Also I have an irregular heartbeat which used to bother me a lot, but it stopped when I gave up sugar and caffeine two years ago. But it has come back in the past week.

I am eating about 50-60 net carbs a day (mainly from fruit, vegetables, and a small bowl of oatmeal each day), lots of protein, and lots of water. Making an effort to get enough sleep but still feel really tired. I am lifting weights three times a week and doing cardio 5 times a week. I would hate to cut back on the cardio, it makes me feel really good to do it, but I'm concerned about my heart beating so fast.

I'm not taking supplements, but I read Doreen's post about potassium & magnesium and according to Fitday I'm getting more than enough potassium & almost enough magnesium.

I would really appreciate some advice on whether I need to be worried about this, do I need to cut back on exercise or change my diet in some way. Here's a link to my public Fitday, (though I sometimes forget to fill out the whole day):
http://fitday.com/WebFit/PublicJour...l?Owner=ovenall