Green’s Dictionary of Slang

1. to experience a state of (usu. meditation-induced) ecstasy; thus blissing out/blissout n., a state of ecstasy; thus blissed (out) adj.

1973		Newsweek 19 Nov. 157: Initiates learn to see a dazzling white light, hear celestial music, feel ecstatic vibrations [...] The process is called ‘blissing out’.
1990		J. Wambaugh Golden Orange (1991) 151: Can’t you jist see me all blissed out over a new study on slime moulds?
1990		T. Winton Human Torpedo 122: I look at seventeen year olds [...] and they don’t looked so blissed that I suddenly want to be like them.
1999		N. Cohn Yes We have No 158: Still flailing their arms and blissing out.
1999		Guardian Guide 26 June–2 July 5: A bit too blissed out on that yoga.
2004		A. Kleinzahler Cutty, One Rock (2005) 86: But how on earth did he [a bar owner / bartender] manage with the hippies and their Jesus hair, tatterdemalion outfits, and blissed-out smiles?

2. as sense 1, with the pleasurable intoxication induced by drugs; thus blissed-out/blisted adj.

1995		J. Stahl Permanent Midnight 179: When I was loaded and blissed-out enough to emerge [etc.].
1995		L. Stavsky et al. A2Z 8/2: blisted – high on a smoked drug: He was blisted on that blunt for hours.