A Silver Alert was issued Thursday for a missing Plainfield man who family members worry may have suffered a medical emergency while driving.Morgan Johnson, 27, was last seen at 11:45 p.m. May 18 leaving the Value Place hotel at 6295 Gateway Blvd. He lived at the hotel and worked at nearby Brightpoint Inc., police said.Plainfield police Detective Joe Aldridge said it's possible Johnson, who has a medical condition that requires him to take medication to prevent seizures, may have had a medical emergency while driving."We're asking anyone who can look down in the ditches and see if they find anyone like that on the side of the road," Aldridge said last week.Aldridge said there's no reason to suspect foul play in the case, but said there's also no reason to explain why Johnson would just take off.The last time Johnson was heard from was May 20, when he called his mother, friends said.Most of his belongings were found in his hotel room and his bank accounts have not shown any activity since he was last seen, they said.Johnson is black, 5 feet 8 inches tall, 155 pounds with black hair and brown eyes. He was last seen wearing blue jeans, a sweater and a black leather jacket.He is believed to be driving a 1995 four-door white Pontiac Grand Am with Indiana license plate No. JS1830.Police said Johnson may be unable to communicate due to a lack of his needed medication.Johnson's friends and family have set up a Facebook page to raise awareness about his disappearance.Anyone with information about Johnson's whereabouts is asked to call Aldridge at 317-839-8700 or Plainfield police at 317-838-3565.