I swallowed a lot of mouthwash this morning. will this lead to sickness?

Usually not: Usually this does not lead to sickness. There is alcohol in the mouthwash, but it's a lot less than beer or wine. If there is Fluoride in the mouthwash, avoid drinking milk because milk and Fluoride can lead to vomiting.

Mouthwash swallow: Probably not if the swallow part is accidental .But if this is intentional, then it depends what other medicines were swallowed too? Only you know. If uncertain consult an er/md really soon. Probably with out delay. Best bd.