I'm interested to know what happens if you swallow an invisalign attachments?

Nothing: If it goes into your stomach if you breath it into a lung , there can be problems.

Nothing bad: They will come out through your digestive process. Nothing to worry about. But see your orthodontist to have them replaced.

Should be OK: Like any roughage, will work out all right in the end. Inform your Orthodontic Specialist right away. If you don't have attachments, there's nothing for the trays to latch on to, therefore teeth will not move as planned. Need repairs now.