Blueberries are very healthy for you and contain antioxidants.
But eating too many blueberries may give you diarrhea, stomach aches etc.
And I've heard that you could get food poisoning from too many blueberries but you would have to consume huge amounts of blueberries before it got to that point if ever.
It's impossible to really eat way too many blueberries that can make you really sick.
If you've eaten a lot of blueberries and you now have got a stomach ache or diarrhea then just cut back on the amount of blueberries you eat.
Otherwise eat as many as you like since it won't do you much if any harm other than the stomach ache and diarrhea or digestive issues.