Long term, energy breeds energy. 

If you push your physical limits in training- get hot and sweaty and out of breath- you will have more energy in day to day life. You will speed up your metabolism, you will burn fat, you will increase your aerobic threshold, you’re using your sympathetic nervous system. Basically, it’s all kinds of good for your heart and your body.

My rule is as long as half of your brain is telling you to stop because it’s horrible and hard, and you push through that, then you are getting fitter and stronger. 

If you’re not used to high intensity training, chances are, the first bit can feel a little stressful as effectively your body goes into fight or flight mode. Power through this bit and learn to move with speed and control and the endorphin release will feel amazing.