I actually think it is a positive when this happens to us in friendlies. I think being good at anything takes practice. So when you start playing bad in friendlies it is the perfect opportunity to figure out what is making you play bad, what makes you start to play better, and then practice doing that, so in tournaments you will be ready. I think if you just always take a break when you are playing bad it will hurt you in your tournament performance when you cant just take a break.
Using my personal experience as an example. I would jump in and start and try to play like I had been playing the day before (after an hour or so of warming up), I would just be trying to move too fast and would just be getting ahead of myself mentally. I realized I would have to slow it down and focus on each move as it was happening and not on anything else. Then I would slowly start to warm up until I was moving fast and thinking fast like the day before.
This is something I have just started practicing this year. I felt like I had plateau'd the year before and took a bit of a break (because I had to work and then traveled to Asia, not because I forced myself to or anything). I realized why I was not improving. It was because I was not focusing and just being lazy when I played, when I started playing bad I just didn't care and let myself play bad.
You have to focus even if you feel lazy, you have to push through playing bad not just take a break. It is like working out, if you always stop right when it gets hard, right before you start to sweat, you just aren't going to improve. I think this issue while it seems like such a small thing is a huge factor in improving your overall skill level.
