2002 Vauxhall Astra engine cooling and electronics immobiliser lights

Engine cooling and electronics immobiliser lights come on now and again and the rev counter drops to zero and the car goes into limp home mode. Have checked coolant level which is ok. car runs at normal temperature. If I carry on driving, the lights go out and all is well again, until the next time. can do it 2 or 3 times in a 20 mile trip.