A teacher battling cancer ran out of sick days. School employees showered him with theirs.

Teacher Robert Goodman ran out of paid sick days fighting cancer. In four days, his colleagues donated enough additional sick days to cover an entire semester.

(CNN)The chemotherapy dripped through a catheter in his chest. Cancer patient Robert Goodman had burned through his paid sick days while undergoing surgery and chemotherapy for colon cancer.

The Florida public school teacher figured he needed at least 20 additional sick days to deal with more chemotherapy, days he just didn't have. So on July 23, right there in a room at Tomsich Health and Medical Center of Palm Beach County, Goodman took a selfie, posted it on Facebook and appealed for help.
Within four days he had enough sick days to cover an entire semester.
    "I couldn't believe it happened so fast," Goodman, 56, told CNN.
    Teachers, staff members, administrators and even lunchroom workers who pay into the Florida retirement system transferred 75 sick days to Goodman.
    "Educators all over the country were reaching out to me to donate their sick days, even professors over at Florida Atlantic University," he said. "I felt guilty because I knew there were people who had it much worse than me."

    A terrifying diagnosis, a stunning response

    Goodman, who has taught history at Palm Beach Gardens Community High School for 23 years, learned he had stage III colon cancer in April. "It was terrifying," he said.
    He began documenting his journey on Facebook.
    "It was the easiest way to let people know how I was feeling and at the same time inspire people who were going through something similar," Goodman said.
    The response to his appeal for more sick days was remarkable.
    "I wasn't surprised that teachers were giving. Teachers are always giving all the time," he said. " When one of their own needs help they'll always step up.
    And there was the outpouring of support from students.
    "Students sharing stories of how I've positively influenced them was a good reminder of why I chose to teach and why I can't wait to get back," Goodman said.

    Missing school, but still teaching a lesson

    During his cancer battle, Robert Goodman finds solace in writing and recording music at PeaceField Studio.