2005 Tucson, 78k miles. Fuel gauge light came on- it was accurate. Filled the tank 5 miles later. Started car and realized the low fuel light was still on and gauge read nearly empty. Drove 100 feet and parked. Turned off car and restarted. Same issue. Turned it off again and tried to restart. Car completely dead- even interior lights. Battery was replaced this summer- alternator checked out fine at that time. Waited 10 mins and tried to start. Started normally and fuel tank shows full. Check engine light was never on. Low fuel light now extinguished. Clock reset to 12:00 so electrical system/computer must have been dead. Drove home 1/2 mile safely. Diagnosis?