I doubt that One-a-Day Vitamins can cause any problem with sleepiness or digestibility.
We've all had sleepy days and fatigued workouts...it comes from being human!
I once bought the "chewable" Vitamin C...the big mixed citrus flavored jobs.
They were so delicious, I ate the whole bottle in two sittings.
Not a good idea, so I stopped picking them up from the $.99 bin.
I have the same problem with antacids but stop at 6 if I feel heartburn...but its HARD to top!
I guess I need to buy them in "FEET FLAVORED" so that I take them as directed.