I have also started taking NAC about 2 weeks ago. I take 600mg once a day in the morning.
What I started to notice shortly after is being very sleepy during the day, also having a really fast heartbeat in the morning after I have taken it. My heart beats normally about 57 beats per minute, and now it went to 90 for a couple of hours.
Also what I noticed is waking up more sleepy and drowsy.
So I have stopped taking it. Im not going to take it again.