MBP freezes for 30 seconds all the time since this afternoon
@Tetsujin is completely correct about the disk. My first hope is that you have a recent backup. If you don't, try to get one, but if the disk is actually the source of the problem, getting a new backup may be difficult or lengthy.

If you don't have a recent backup, you Time Machine with an external hard drive will produce one for you. My preferred first-line-of-defense backup, however, is a clone, which I create with Carbon Copy Cloner. Once this software has successfully created a clone, you should be able to boot from it with little noticeable difference from booting from the internal drive (other than, hopefully, a lack of trouble).

Once you have a clone and have booted from it, if that confirms that the problem has been resolved you can be pretty sure your hard drive is the problem and take steps to replace it.