Anyone know if switching BACK to fossil oil after using synthetic would cause any problems?

I only put about 3500 mi/yr on my truck in about 5 mile increments. So... I end up changing the oil based on time (every 6 mo.) rather than mileage.

Is it really worth using synthetic at about three times the price?

Is there any harm going from synth to fossil?

TIA, XLT_D.