Caffeine plays a major role in insomnia, low-feeling tone, and other effects, especially if we're sensitive to it. While it does pick us up for a short while, it drops us much lower in feeling after the effects of caffeine wear off.
I think it's best to remove it entirely from our diets, frankly. (That, and
tea and chocolate; they all react very badly on people who are sensitive to them.)
Alcohol is another we should remove. It's a depressant and the after-effects are as strong as caffeine.
Please read
http://www.caffeineallergy.com ruthwhalen That's the best article out there that I know of to convince one of the seriousness of caffeine allergy.
Take good care of yourself.