This is typically a sign of dehydration, which happens to be one of the leading causes of both fatigue and perceived hunger pangs.
As for the pangs, these are simply a response by the stomach when the body needs either food, water, or both. But because the sensation is exactly the same either way, it can trick you into thinking you need food, when it's really a matter of getting more fluids.
Additionally, the effects of stimulants are greatly diminished during a state of dehydration. For instance, many times people will be drinking cup after cup of coffee but getting more and more tired. This happens for a number of reasons.
First, caffeine blocks adenosine, which is a neurochemical that makes you sleepy. With adenosine blocked, epinephrine (natural adrenalin) levels rise and make you more alert. However, after consuming too much caffeine (and/or other stimulants) your body tends to increase the production of opposing chemicals to help slow or level-out rapid heart rate and blood pressure, which then makes you tired, no matter how many more stimulants you consume. At this point, the body needs a break from all stimulants so that it can properly reset.
Second, water makes up the majority of your blood and other bodily fluids, and even mild dehydration can cause blood to thicken, forcing the heart to pump harder to carry blood to your cells and organs, which can result in fatigue. Also, ample fluids keep energy-fueling nutrients flowing throughout the body.
On top of all this, stimulants themselves are diuretics, which promote an even more dehydrated state. It can turn into a real vicious cycle when proper hydration is not handled both before and during the consumption of stimulants.
As recommended by The Institute of Medicine, adequate intake (AI) of fluids for women is about 9 cups (2.2 liters) of total water per day. For men, it's roughly 13 cups (3 liters) per day.
Also, hydration starts the day before, rather than the day of. And you can very well be dehydrated long before you are officially thirsty. So, if you plan for any sort of fitness routine, or exposure to hotter climates, the time to start getting your 2.2-3 liters of daily water intake starts no later than the day before, and should continue throughout and beyond.
For further concerns, please consult with a certified physician.
The Institute of Medicine