Yes it absolutely is. May I assure you that this will only be temporary and happen in waves throughout your progress. For me it was anxiety and depression and will be different for you on when and how much intensity is felt. Make sure to get some fresh air daily and meditate if need be. A lot of fapstronauts have taken up some meditation practice to have more control over the brain during this challenge. Control is key!
I can absolutely say first hand that it comes and goes. It hit me pretty hard with the anxiety and it is not something I ever had a problem with at any other point in my life. Having your heart race and feeling crippled by fear absolutely sucks. I also had some very significant mood swings a week or so ago. I am on day 26 and I have only had a handful of days where I felt good all day. Most recently I am on a stretch where I just can't sleep through the night anymore. Depending on the length and types of exposure you previously had will certainly play a roll in recovery. Recovery is definitely different for everyone. Hang in there though. The anxiety, mood swings and such will pass.
I had all those symptoms when I rebooted the first time. They start to go away as you get further into it. Most of my serious symptoms were gone by Day 30. i relapsed at Day 96 and am two weeks in and am beginning to experience some symptoms again. My addict brain is trying to convince me to PMO but I hate it and want to stay sober and get past the symptoms. I know if I could get to Day 96 once I can do it again and even go further. So can all of you.