When the Southern states succeeded from the Union, there members resigned from the House of Representatives and the Senate. How did the Northern states deal with this during the Civil War? Were those seats (namely in the House) split amongst Northern loyal states? Were they kept open in case a Southern state decided to send representatives? Namely, how did this impact the election of 1862 when the Civil War was happening?

Also, I'm assuming the answer will be that since the government considered it a rebellion and that the Confederates states were not recognized as a separate country, the seats were likely left empty. Why then during Reconstruction was it not as simple as once the War ended allow them to send representatives back?

I apologize if this seems overly simple. I haven't been able to accurately put my thoughts on paper, but I am really curious about this philosophical dealing with the Confederate States in terms of the Congress.