Peugeot 307 sw 59 plate warning light 'check oil level' help?

3 days ago my Peugeot 307 sw went into economy mode by itself read up what it meant still no wiser and hasn't done it since. However same day got maintenance light on and on the dashboard where the radio etc display is 'check oil level' Took to garage topped oil up still stayed on a few mins before going out. Garage then did a diagnostic check came back some about oil gauge sensor. He did say try dealers who will an indepth diagnostic just to be sure. Booked in at dealers today. Last night went to car to check if it was still the case no warning ights on and all working fine, checked again this morning all fine so cancelled the 2nd diagnostic check at dealers. What happened? anyone know why it said it even after oil topped up and now it's gone again? Should I still have the dealers do a check at cost of £100 just to tell me nothing wrong or get same result as my own garage