Passed out in orthodontist office today rushed to hospital but nothing found. what happened?

Syncope: Not an uncommon thing to happen. It is called syncope cause by nervousness which overstimulates a large nerve called the vagus nerve. It controls many important functions in the body....Heart rate breathing rate and more. Stimulating this nerve can cause you to pass out.

Depends: Could be anything. Nervous? Low blood sugar? Low blood pressure? Dehydrated?

Possibly: Vasovagal syncope but would recommend discussing with your physician.

No idea: You could have passed out for many, many reasons, but it likely had nothing to do with the orthodontist.

Wow: Hard to tell, but not orthodontic related. Maybe an allergic reaction to a smell, etc. In office or anxiety.

Wow: Not due to Orthodontic Treatment. May be due to Orthostatic Hypotension (sitting up too fast), anxiety, medications for non-Orthodontic problems, low blood sugar, (rarely) allergic response to environmental stimulus, or many other things. Hopefully the cause was benign. Probability is that ER Exam would have revealed anything problematic, so you should be OK.