Michaels, who underwent an emergency appendectomy April 12, reportedly was experiencing a severe headache late Thursday night, resulting in the 47-year-old singer being rushed to an undisclosed hospital where doctors diagnosed him as suffering from a massive subarachnoid hemorrhage – bleeding at the base of the brain stem – according to People, which reports Michaels is currently listed in critical condition.

“After several CAT scans, MRIs and an angiogram, [doctors] decided to keep Michaels in the ICU and are running tests to determine the cause. [It] will be touch and go for the next few days while he is under intense observation,” a source described as “close to the situation” told People.

Michaels, who is in the midst of a solo tour, was about to go onstage in San Antonio April 11 when stomach pains the singer had earlier thought to be the flu finally got the best of him, resulting in the singer undergoing an appendectomy early the next morning. Because he’s diabetic, doctors transferred Michaels to a facility specializing in helping patients afflicted with the disorder.

So far, Michaels representatives have yet to comment on this latest development.

Click here to read the complete People article.