I took Vyvanse several years ago, too, to increase my energy level. It worked for awhile. But then I started becoming exhausted after taking it. It felt like I was crashing from drinking a pot of espresso. I was exhausted and jittery at the same time. My theory is that Vyvanse was too much of a stimulant for me. My body responded by trying to slow itself down, hence the exhaustion. I would feel okay when I woke up, but 20 minutes after taking the Vyvanse I was exhausted. So I went off of it. Since then I was never as tired as before. I think it change my brain structure or something.