Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for trouble breathing, a seizure, collapse, severe confusion, inability to awaken the person, or rapidly worsening symptoms.
And for anyone, someone who:
Seek urgent reassessment for worsening vomiting, persistent diarrhea, reduced urination, increasing weakness, new confusion, or difficulty keeping fluids down.
Arrange routine medical follow-up if digestive symptoms continue, weakness does not resolve, or the person is not returning to normal eating, drinking, urination, or activity.
Follow-up may include checking hydration, kidney function, or electrolytes after a more significant illness.
The article also says
Follow the observation plan given by the poison center or treating clinician.
After a mild exposure, this may include watching for vomiting, diarrhea, unusual sleepiness, confusion, weakness, or vision changes during a specified period.
If vomiting or diarrhea occurred, fluids may need to be replaced gradually.
A clinician can advise when normal food and activity may be resumed.
Do not return to foraging or eating from the same plant unless it has been reliably identified by a qualified expert and confirmed appropriate for food use.
Every sign above is quoted from the sofidex article on Black nightshade poisoning. If you are not sure, err upward — it is always reasonable to be checked.