The 74-year-old was taken to a private clinic after falling ill in Mascarat on the Costa Blanca complaining of eye problems, his son John said.
Tests were inconclusive and he was discharged to return to his family.
Born in Northumberland, he played for Leeds United and became manager of Middlesbrough, Sheffield Wednesday, Newcastle and the Republic of Ireland.
He only had one year in the hot seat at SJP, and walked out on the club after a pre-season friendly against Sheffield United when fans chanted at the sale of Chris Waddle.
Former Mackem Eric Gates often tells the story of when Charlton tried to sign him for Newcastle from Ipswich.
"He phoned me and said he would take me for a slap up meal to talk about a transfer. He bought me a cheese sandwich in a service station."