Symptoms vary depending on what is causing the illness. They may begin within a few hours or a few weeks depending on the cause. Common symptoms are: 
Upset stomach.
Vomiting.
Diarrhea.
Diarrhea with bloody stools.
Stomach pain and cramps.
Fever.
Headache.
 Less often food poisoning affects the nervous system and can cause severe disease. Symptoms may include: 
Blurred or double vision.
Headache.
Loss of movement in limbs.
Problems with swallowing.
Tingling or numbness of skin.
Weakness.
Changes in sound of the voice.
