Green’s Dictionary of Slang

1. (orig. US) enjoying oneself.

1968		‘Hy Lit’ Hy Lit’s Unbelievable Dict. of Hip Words 19: groovin’ – To be hung on a pleasurable thing [...] which you find enjoyable and relaxing.
2000		S. Maloney Big Ask 43: I gave myelf over to a little gentle grooving.

2. (drugs) the state of having an enjoyable time while using a drug.

1969		R.R. Lingeman Drugs from A to Z (1970) 105: grooving [...] Becoming intoxicated on a drug, as in ‘he was grooving (on) pot’.
1988		Ice-T ‘I’m Your Pusher’ 🎵 Groovin’ like I see you doin’.