Steering problem
2002 Citroen C3 6 cyl Two Wheel Drive Manual 100000 miles

Hi
I have a 2002 citroen c3 1.4 hdi.. earlier today after i had been driving for approx 20 mins the steering became very heavy quite suddenly. I had almost got into my workplace carpark so continued and parked the car. Later on in the day, at the end of work, I drove home and the steering was working fine again . What could be the problem ? I know the c3 has an electric power steering system, so it cant be an empty fluid reservoir. Will this happen to the car again ?
Thanks Joe