It is possible that you experienced a vasovagal response when putting in your new dental trays, which can cause dizziness, sweating, and fainting. This is a fairly common phenomenon and usually not a cause for concern unless it happens frequently. Other possible causes could include hypoglycemia or low blood pressure. If you have other health issues, it may be worth consulting a doctor to determine the exact cause. If this situation happens again, try sitting down and taking deep breaths to prevent fainting. Additionally, if you suspect hypoglycemia, consuming something sweet like orange juice may help. It is important to monitor your symptoms and seek medical advice if needed.