Purity

I was in bed and I had a sexual thought. When I was in bed it somewhat felt like there was some wetness after having the sexual thought.

However upon getting up and checking my underwear there was absolutely no visible sign of either mani, mazi or wadi whatsoever.

Therefore is it correct/safe to assume that no liquid was released from the penis and that there is no need to do Ghusl and that there is no need to change my underwear as it is still paak?