- As long as you are wearing tefillin you may not sleep. The Gr”a says you can nap for 47 seconds.(ShA1 – MB 4)
- It is forbidden to have hessech hadaas while wearing tefillin. This includes joking and a lightheaded mood. The best way to do the mitzva is to constantly remember that you have tefillin on you – so you don’t come to wrong thoughts. However, during daavening and learning you need not put your mind on your tefillin. (MB3)