So, the way I've understood it, "sensory disturbances" can be categorized as follows:
Any sensory experience that isn't real goes under "sensory disturbances" in this diagram. If this unreal sensory experience is a distortion or misunderstanding of real, external stimuli, then it falls under "illusions". If the unreal sensory experience is generated in the absence of external stimuli, it is a hallucination. If the person having the hallucination believes in it, it is a true hallucination. If not, then it is just a hallucination.
So, if a person perceives an object to be a different color, whether it is due to an altered state of consciousness, or if it is due confusing circumstances, is this an illusion or a hallucination? The object is real, it does have a color (which in a sense isn't real and potentially experienced differently by different people), and the person sees the color differently than what they normally would. Is this external stimuli being distorted/misinterpreted, or is it a hallucination being superimposed upon or merged with an external piece of stimuli. What if the subject doesn't see a different color, but rather a different shade of the same color?
If a taste is changed from e.g. sweet to salty is it an illusion or a hallucination? If an object is perceived to move when it is not moving, is it an illusion or a hallucination.
At the heart of these questions really is the question: does in the absence of external stimuli necessitate that the hallucination not involve external stimuli, or not depend on it? If the object is falsely perceived to be moving, it involves it (and in a sense depends on it too), however, it isn't the nature of the object that causes the sensory disturbance, but rather an internally created disturbance (the perception of motion) instilled into the object. But since that percept of motion, although originating from within, modified an external stimuli in order to give the final experience, is that experience then an illusion due to it coming in the form of distorted, external stimuli?
Basically, I'm wondering about the nuanced border between illusions and hallucinations, if there even is one. If there isn't one, and there's a large grey area between them, then how does one differentiate between the two different categories proposed for the class of drugs that are hallucinogens? The broadest definition includes all drugs that sensory disturbances, and the most narrow definition is limited to those that produce hallucinations. How can that discussion be had in the event that there is a large gray area between illusions and hallucinations?