Why do stimulants make me sleepy?

Need more info: Which stimulants are you referring? What is time frame (i.e. Immediately after taking or several hours later)? If you are taking rx talik to your prescribing doctor. For some people (not only add), stimulants slow down thought process, but for most they accelerate. Most are short acting and feeling sleepy is part of withdrawal. Eg 3-4 hrs after coffee.