Meaning of “GanGimari(ガンギマリ)”

“GanGimari(ガンギマリ)” means euphoric (due to taking drugs) or looks like so (even if he/she doesn’t take drugs), kind of…
“Gan(ガン)” is an abstraction for “Gangan ni(ガンガンに)” which means “super” or “strongly” in this case, maybe. This is an onomatopoeia.
“Gimari(ギマリ)” means “drug is working”, this comes from the verb “kimatteiru(キマっている)”.

Example Conversation

A: What? You didn’t sleep at all last night?
B: Oh, yeah. But I just took a lot of caffeine, so I’m fine.
C: Your eyes are wide open.
A: You’re totally “GanGimari(ガンギマリ)”.

A: え、昨日寝てないの？
B: あー、うん。でもさっきカフェインを大量に摂取したから大丈夫だよ。
C: 目バッキバキじゃん。
A: ガンギマリだね。