If the ringing is in both ears, it could signal an over dose of medication, such as aspirin. If the ringing is on one side along with decreased hearing, it could signal something more important like a neurological tumor. If ringing persists, see a doctor. Dry mouth could be related to your medications and medical history. Some people naturally have dry oral membranes, so it's nothing to worry about.
Cotton mouth can be a side effect from medications such as anti-histamines.
It also can be due to de-hydration and may signal some underlying problem. It's a common side effect of medication, but it also can be seen with dehydration or neurological problems. Eyelid twitches are experienced by most people at some point and are virtually never anything to worry about. A racing heart can be a symptom of anxiety, but there are many serious conditions that can cause abnormal heart rhythms. It doesn't always indicate a problem, but you should see a doctor.