I grant that hallucinations need not be visual only - for example, there could be aural hallucinations, hearing something that isn't there; but hallucinations are always perceptual. Since `sensing a presence' without the use of sight or hearing isn't a perceptual experience, having the feeling of euphoria can't strictly be classified as a hallucination. Yet, we can't just put it down to a person's imagination, either, since the cause of the feeling can be identified.
It's just another example where our usual linguistic notions are challenged by a special case. Interesting stuff.