To begin with first, illusions and hallucinations are different.
An illusion is a:
a distortion of the senses, revealing how the brain normally organizes and interprets sensory stimulation.
while a hallucination is a:
perception in the absence of external stimulus that has qualities of real perception.
A hallucination is basically perception of objects that do not exist.
But Vishishtadvaita Vedanta believes that you cannot perceive unreal objects, but only real objects, however limited that perception might be. For example, mistaking a rope for a snake at night or thinking pearls are silver are actually illusions: perceptual distortions of real objects. A rope has "snake-like" qualities, and due to limited perception, you see the rope as a snake, but upon closer inspection, you see it's just a rope.
A hallucination would be experiencing a completely unreal object that cannot be explained through an illusion. For example, some people who take large doses of drugs claim they can see and talk to people who don't actually exist for the duration of the drug intoxication. They claim that while intoxicated, these people are indistinguishable from real people. They say these people aren't real because undrugged people near them say there is actually no one, and also because these fake people vanish when the drug wears off.
But Vishishtadvaita Vedanta gives good reasons for why we can't perceive unreal objects.
My question is, are these experiences actually hallucinations or elaborate illusions? If they are illusions, what real object would be mistaken for an actual person?
If they aren't illusions, then is the drug allowing them to see things that they otherwise wouldn't? Could they be seeing ghosts or spirits? They are known to cause people to see things and also have the power to change forms/shapeshift. If this is the case, why do ghosts only appear when people are intoxicated with drugs?
EDIT: Could it also be that "hallucinations" is actually the state between wakefulness and dreaming? The Brahma Sutras give 5 states of consciousness: waking, dream, sleep, coma, and God realization. So in these drug-induced trips, could it be that the individuals are awake, but also dreaming, and they combine their dreams with wakeful consciousness, leading to a hallucinogenic trip?
EDIT 2: In Ramanujacharya's Sri Bhashya, this is what Ramanuja says in the Mahasiddhanta part, section 11 All Knowledge Is of the Real:
Brahman alone is the creator of everything in this world, be it in the waking or in the dream state. The waking state is experienced by all souls but the dream world is experienced by the dreaming individual alone as it is meant for him alone and is created by the Lord as a fruit of that particular individual's merit or demerit. Similarly in the waking state also certain things are created by the Lord as are experienced by all, while certain other things are created in such a way as to be perceived only by particular persons and to last for a limited time only, and it is this difference between objects of general perception and objects of perception of particular beings, which makes the difference between things sublating and things sublated. Thus all perceptions are real and all knowledge is real and there is nothing like unreal object or wrong knowledge.
Is Ramanuja hinting at hallucinations here or illusions?