Not saying this doesn't apply to 11/6/2018, and if so, that's a bit chilling. BUT, there were actually elections on Tuesday of last year. November 7, 2017 (two days after the Q post) was an "off-year election" with minimal (albeit negative) impact.
There was a net loss in the Senate with 1 Republican seat lost and 1 Demoncrat seat gained. There was no net change in the House. At the state level there was also 1 Republican seat lost and 1 Demoncrat gained.