Is it worht it? Well, my dad has always been very healthy. Exercised and ate right. Well, he did get diabetes, but not until age 60. His sister's had it as long as I can remember. He did need to have by-pass surgery at 65, although he never did have a heart attack. The doctors told him he would have had a heart attack 10 years earlier if he had not taken such good care of himself. Yup. His sister had by-pass surgery about 10 years before.
I say it's worth it. However, it sounds like you're generally eating right and exercising. So, you know it's worth it. I agree with others. Maybe you just need to shake up your routine a bit. I've heard that putting in small workouts throught out the day is just as good for you. However, if you're looking to burn fat, you really need to get your heart rate up for more than 20 minutes at a stretch.
We all get dissappointed at times. You'll get back in the swing of things again!