Raila was rushed to the hospital in the morning after complaining that he was feeling unwell.
"He was treated and later discharged. He is at home and will continue with his activities tomorrow," Dennis Onyango, his spokesman, told the Star on Wednesday.
"He also underwent a check-up. It is normal."
Onyango added that the Opposition chief was out of danger and will leave for South Africa on Thursday to visit his daughter Rosemary, who is sick.
He was to address governors at the 4th Annual Devolution Conference in Naivasha but will be represented by Ford Kenya leader Moses Wetang'ula.
Raila was last seen at former Nyeri Governor Nderitu Gachagua's burial on Monday.
At the burial, he castigated counties for misusing devolution funds citing unwarranted foreign trips.
The ODM leader said bench marking and bonding sessions that MCAs use to hold governors at ransom were unnecessary.
-The Star