It feels like a new, meaningful merger or acquisition is announced daily-- mostly because companies have been busy making deals. And, while transaction volume has rebounded nicely from a recent low in early 2013, May's sharp drop in the value of transactions looks an awful lot like the one seen in June 2007 that preceded the gradual decline into 2008/2009 lows.
Certainly, one month's data does not guarantee a similar situation-- but it does bear watching.