State Rep. Darren Bailey, R-Xenia, fainted about 1:45 p.m., Republican leader Jim Durkin said.
Bailey was wearing a mask when taken ill.
Bailey is awake, and paramedics have taken him to a local hospital.
Durkin said Bailey had been suffering some gastrointestinal issues and fainted.
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Durkin asked for a silent prayer and wishes for a quick recovery after the incident.
Bailey's office issued a statement Sunday that read:
"State Rep. and Senator-Elect Darren Bailey (R-Xenia) experienced a minor medical issue today during proceedings of the Illinois House of Representatives.
Rep. Bailey fainted but is now doing well and being treated at a local hospital. He is looking forward to returning to work as soon as possible. The Illinois House is meeting at the Bank of Springfield (BOS) Convention Center, the host site for the 101st General Assembly's "lame duck" session."
Bailey, a downstate Clay County Republican who represents the 109th House district, sued Gov. JB Pritzker last year, claiming Pritzker's emergency powers with regard to COVID-19 had only limited power and violated his civil rights.
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In May of 2020, Bailey was escorted from the House floor for not wearing a mask, which was mandatory under House and Senate rules established because of the pandemic.
Pritzker wished Bailey a speedy recovery Sunday afternoon in a tweet.
Bailey was elected to the Illinois Senate in the November election and will be sworn in on Wednesday as a state senator from the 55th district of Illinois.