Could you use more calm and joy in your life? Which fellow above would you like to feel like? If it's the one on the left, Yoga won't help. However, if it's the smiling guy, then Yoga has a place for you. But as with anything in life, overdoing it can wreck havoc!
Several weeks ago, I attended a Yoga Workshop in Chicago. We worked with the bandhas (energetic locks in the body) which has the ability to increase the prana (energy) that you have. It can be a heating and healing experience. But overdo it, and you mess with your nervous system. One of the women there, had trouble sleeping for over 6 weeks due to using Maha Mudra, a powerful use of the 3 main bandhas every day -- during those same 6 weeks! Perhaps, she didn't realize the connection between her increased prana and the insomnia--in which case she shouldn't have been practicing the technique at all.
My advise? Look at your life. What's working? What's not? Are you loving and patient? Are you stressed and frazzled? Taylor your practice to match what your needs are. If you are lethargic and tired a lot, then a more active and stimulating practice is in order. Don't go overboard and end up wired. Within a week or so, you will most likely find a balanced practice that works for you. Yoga asanas (postures) and pranayama (extending life force with breath) that are active and challenging will bring more energy to you body. On the other hand, if you are constantly on the go and your body and mind are crying out for rest, then slow moving asanas and cooling pranayama, such as Sitali or Sitkari, are in order.
So, look at your practice. How do you feel before you begin? How do you feel afterwards? Make sure that what you do on the mat aids you in your life.
Remember Yoga has the ability to transform your life and provide greater health and happiness. Use it wisely.