Green’s Dictionary of Slang

1. heavily intoxicated by drugs.

2000

R.A. Spears NTC Dict. Amer. Sl. 453: vegged out mod. debilitated by drugs or alcohol.

2. exhausted.

1985		Eble Campus Sl. Oct. 10: vegged out – exhausted. ‘The entire class was vegged out following their final.’.
2008		B. Shoup Èverything You Want 58: When I get home, Mom and Jules are vegged out, watching a movie on TV.