Game Lag

[Gabbbb]

Hi there,
i'm new to this forum but i've been playing this game from months already in boring times during my job. It often occurs that the game starts lagging in a pretty strong way, making it kinda impossible to play as the timing of the song it gets out of synchro with the arrows ofc.
That's my average speed here so i don't think it's a connection problem, my laptop has a dual core processor and 4gb ram. What might it be the problem? Thanks for your help