Haywood was told last week he had made the hall, but was later informed he had not, leaving him upset about the misunderstanding.
"I don't know why there was confusion," Haywood, who played for five NBA teams, told the Las Vegas Review Journal. "Someone from the NBA told me I was in, then I found out Friday night that I wasn't in.
"This is so embarrassing. My stomach has been so bad I can't eat, I can't sleep. This isn't a punch in the stomach. It's below the stomach."
The official announcement of this year's hall selections will be made on Monday in Atlanta.
Meanwhile, with the clock ticking down in the NBA regular season, injured Chicago Bulls point guard Derrick Rose remains noncommittal about his return.
Before the Bulls' shootaround on Sunday, Rose continued to say he is not sure when he will play again. But he is not ruling out playing this year.
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