Leaving a tampon in place is not a rare event. Condoms fail or break in up to 20% of cases.
Leaving a foreign body in the vagina can produce severe irritation and infection. One of the most severe type of infection is called Toxic Shock Syndrome. The most common bacteria causing this infection are Staphylococcus aureus and Streptococcus pyogenes. They produce a toxin which can be fatal if a tampon is left in for too long.
Signs and symptoms can include a rash resembling a sunburn, high fever, low blood pressure, malaise and confusion. The vulva can become severely inflamed, red, swollen and tender to the touch. Other more dramatic evidence is a strong foul smelling yellowish-greenish discharge.
Treatment of either a retained condom or tampon involve the obvious removal of the foreign body followed by a vaginal wash and antibiotics.
The best way to handle this situation is not to wait and see what happens. Although it may be embarrassing, your gynecologist has seen these problems many times before and it is relatively fast and easy to treat these situations by your doctor.