If it were me, I would probably sit down with my supervisor--if I could find a relatively stress-free moment, for both of us--and say "Look, I realize last week was pretty terrible. I know I bungled X and Y. I'm struggling with Z and Q. Can we talk about this?" I would adopt a friendly, apologetic, constructive tone (regardless of my feelings about last week or said supervisor).
EXTREMELY sage advice. Everyone has a bad week on occasion. Whatever cosmic confluence caused the problems may well melt away over the weekend. Nothing you can do in themeantime.
I had a similar situation years ago, not in academia, but the supervisors (yes two) were really ticked off at me. I went in and just put it on the line: no excuses, no apologies, just an honest assessment that things got the best of me and that my biggest error was in NOT asking for advice/assistance when I needed it. YMMV, but I think that this is a good approach.