Sanders had a series of campaign events scheduled Wednesday in Las Vegas and more scheduled Thursday in California, according to Cox Media Group's Jamie Dupree.
Sanders recently canceled some appearances in South Carolina because he lost his voice. The campaign said at the time he felt fine.
Sanders, the Democratic field’s oldest candidate, sometimes jokingly refers to his age at town halls and other events, especially when interacting with younger participants. His aides have tried to project him as a candidate with energy levels that surpassed his 2016 presidential campaign.
Check back for updates to this developing story.