It could be a few different things:
- Your CPU is overloaded, either because this game is larger than other web games or because you have other applications running at the same time.
- Your Internet connection has a high ping right now. That will always be true for some low-speed connections. However, it can also happen for high-speed connections depending on network traffic, other applications on your computer, or general Internet slowdown in your area.
- One of the above conditions is affecting your opponent. You're both playing together, so if they have a problem with slowdown, you'll notice the effects, too.