Loss of power - 2007 petrol scenic

So, I have a 2007 scenic petrol engine. Over the last few weeks it has started losing power at various times. The engine can be hot or cold. It can be first thing in the morning or it can happen after driving the car here and there for the day. I have to really press the accelerator pedal to the floor and then after a few seconds the cars power will be back and we're roaring up the road. Its happening more and more now. Popped into the garage to see if it might be something simple:crazy: They say its like looking for a needle in a haystack and it could be anything. No dashboard faults showing. Anyone have any idea where to start with this.