Oil pressure guage acting weird lately

[Mick]

The needle of my oil pressure guage is normally just under the first line. Twice in the past week I have noticed it just under the top line ( by the oil can), it stayed there for a few minuites then gradually decended back to it's usual position. I though this might have been caused by a bad electrical contact, but I have made sure this is not the case and it has done it again. Any ideas ?

Thanks

PS The oil was hot when this happened, both times.