Berry Poisoning

If you eat 6 Strange Berries in a day, you will be inflicted with Berry Poisoning! Berry Poisoning periodically deals significant amounts of damage every 8 seconds and typically lasts 40 seconds

Your level of poisoning is indicated by an icon near the bottom right of your hotbar:

A message also appears when you get the effect to notify you!

Resetting my poison level

To reset your level of Berry Poisoning, you must either sleep in a bed essentially skipping to the next Minecraft day, wait until the start of the next Minecraft day, or you can just die and respawn (I personally wouldn't recommend that one)