The Good Morning America anchor fell ill while on vacation in Key West, Fla., she told fans in a Facebook post Thursday morning.
"I began not to feel well. Nothing serious, just under the weather," she writes. "I contacted my doctors and flew back to NYC. They felt it best to admit me into the hospital for a few days. Seems my young immune system needed a little boost to fight off 'opportunistic infections.' "
Roberts, 52, who had a bone-marrow transplant last September after being diagnosed with myelodysplastic syndrome, says last week's setback was minor and not uncommon for someone at her stage of recovery.
"My doctors assured me that this was NOT because I was working or doing too much, too soon," she writes. "It's extremely common, post bone marrow transplant, to have complications. I'm blessed that mine have not been severe."
Roberts says she's now "feeling MUCH better," will relax at home this week, and plans to be back at the GMA anchor's table next week.