Don't know what you call "flat" but it went from $16.80 to $15.50, then went down to $13.5 on monday (an extended weekend due to the 4th of july).
As you can clearly see here, first a significant fall (from ~17 to ~15.5) just before the weekend (on thursday and friday), then completely flat during the weekend (saturday and sunday), then a huge fall down to 11.5 on tuesday and big rise until wednesday evening (GMT).
Mondays are not weekends whatever holiday it is. Weekends last two days - saturday and sunday, and this dip lasted 6 days (you could say it's still going on since it was around a stable 17 for almost a week before that and it still hasn't come back to 17), and it actually completely paused and stagnated during the weekend (I thought that was it, and that it was going to rise in the beginning of the week, but then it started to fall even more).
This weekend completely blasts the theory about weekend slumps out of the water (at least for this weekend). But bitcoin is in truth still too unpredictable for any dependable patterns.
