Maine State Police said a medical issue likely caused a driver to lose control of a fuel truck Monday when it struck a guardrail and a cement abutment before overturning along northbound Interstate 295 in South Portland. The truck had just left the South Portland fuel depot and its entire load of 2,900 gallons of home heating oil spilled onto the road, went into the median and flowed into a drain pipe to the Fore River. Traffic was reduced to one lane in both directions and was expected to continue that way for the rest of the afternoon. The driver of the truck, 58-year-old Dale Brown of Topsham, was being treated at Maine Medical Center in Portland for a head injury and his medical issue, suspected to be heart related. Both were believed to be non-life threatening. Brown is the owner of Dale’s Cash Fuel in Richmond. Cleanup efforts overseen by the Maine Department of Environmental Protection were expected to continue for the rest of the afternoon.