Help I ate a nightshade berry?
Call the national Poison Control Center hotline 1-800-222-1222. They can help you figure out what you really ate and whether you need to call 911 or get to the ER.
Be more careful next time you eat something. A bitter taste is a sign that it may not be good to eat it. The fact that you were able to write this question indicates you won't have any major problem. Just one berry is unlikely to affect you very much.