It definitely seems like participation is down, but that usually happens this time of your. But the other answer is you might have changed your view preferences.
Click My Forums on the top right corner of the window.
then on the left side of the window click of My Preferences.
Scroll down to the General Preferences and see if you possibly
changed Topics per page from the default 20 to 40.
Changed Posts Per Page from the default 10 to 20.
That will make it look like you're suddenly getting only half as many posts as you used to when in fact you're only seeing twice as many posts on the screen before you have to click onto the next page.