Rose, 22, spent Wednesday at Rush University Medical Center for a procedure while he was under anesthesia.
"They put this camera down my throat," Rose said. "It was hard. I was in the hospital the whole day."
Rose thought he had only heartburn early in the week, but his discomfort did not subside.
"I'm feeling all right," he said. "[There's] still pain ... it's real painful for me to eat, drink, swallow, all that stuff, but they gave me some medication for it, and that's what I'm taking right now.
"I had heartburn, they gave me some pills ... thinking that it was going to go away but it didn't. And that's when it really got bad where I couldn't sleep good at night. And I thought I was having a heart attack, and that's when I called [athletic trainer] Fred [Tedeschi]."
Rose, who also missed practice Wednesday, hopes to play Friday when the Bulls host the Orlando Magic.
"I haven't really been able to eat anything so my energy is kind of low, but every day it should be all right," he said. "I guess I've been eating too much spicy food or something like that, because I love spicy food. But other than that I think I've been eating well, besides the spicy food.
"I'm going to have to watch a lot of things I eat now. [Doctors] gave me a list, there's a lot of things on it."
Thibodeau wouldn't rule Rose out for Friday's game.
"We'll see how he is [Friday]. He's better [Thursday] than he was [Wednesday]," Thibodeau said. "If he's better [Friday] he goes, if not, he doesn't."
Rose, who learned Thursday night that he will start for the East in the All-Star Game, is averaging 24.6 points and 38 minutes a game. He has played in all but one game this season.
Rose said he didn't believe the condition was caused by stress.
"No, we're winning," he said with a smile. "We're winning. I'm feeling pretty good right now. I don't got to worry about anything. So stress, I'm not worried about that. Now last year, and the year before that, if I would have gotten one it probably would have been because of stress, but right now, I'm doing pretty good right now. If anything, I definitely have to change the way, what I eat, and that's spicy food."
He said he was surprised to see pictures of the ulcers.
"I couldn't believe it," he said. "Actually, I woke up and the doctor wasn't in there. And my mom had all these types of pictures and stuff of my stomach, showing me where the ulcers were. Actually there were two, a [bigger] one and a smaller one.
"It hit me hard where I thought I was eating fine, but now I got to see. I got to stop eating spicy food."
Charles Barkley, who said Rose is the leading MVP candidate at the moment, said Tuesday on ESPN 1000 that he hopes Rose doesn't get worn down.
Nick Friedell covers the Bulls for ESPNChicago.com and ESPN 1000.