Dealmaking in the U.S. middle market declined in the third quarter, according to this report from Mergers & Acquisition magazine. The slowdown began in the second quarter, as the number of closed transactions declined versus the first quarter. The report notes that it's unlikely that 2015 will produce the level of middle-market merger activity that 2014 saw. 

There are some bright spots, most notably the lower middle-market and family owned companies, which are motivated to sell while the economy is still relatively stable.  The report notes "M&A activity in the lower middle market..appeared to be thriving." The report is linked here