Could invisalign cause nausea for the first few days?

I guess it could: If you are uncomfortable with a foreign object in your mouth, I guess it could cause nausea. Speak to the dentist treating you about your concerns.

Yes, it could: If you are uncomfortable with a foreign object in your mouth, it could cause nausea. Talk to the dentist treating you about your concerns and get some anthelmintic OTC medication. The nausea is transient for a few weeks only. Take care.

Not common but....: Reactions to foreign objects in our mouth vary widely from person to person. First there is the natural protective mechanism which may elicit this type of reaction to varying degrees. Secondly, some people are more sensitive than others to tastes, smells and sensory feelings. What you are experiencing should resolve quickly as your body & mind accommodate to it. If not, speak to your dentist.

Possible: Foreign body reaction. Usually transient. By 3rd day should be diminishing. If not call both your Physician (cold, medication change, food reaction, GERD, etc) and your (hopefully) Orthodontic Specialist or treating Dentist to check appliance.