Hallucination
noun
An illusion you have when you're awake is a hallucination.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
それ、ただの幻覚じゃない？
Isn't that just a hallucination?
彼女は時々、ポッドキャストをレコーディングしている時に幻覚が見えるそうです。
I heard that she sometimes has hallucinations when he is recording her podcasts.
あの森には幻覚を引き起こすキノコが生えていると聞いたことがあります。
I've heard that hallucinogenic mushrooms grow in that forest.