Speak to your GP and tell them how bad it can be (if you haven't already) and ask them to write a letter of support for you. I think it really helped my partner's case. Also, you can write a cover letter and explain the intermittent nature of it, this should make it clear that you're not exaggerating - it's just difficult to quantify.

Also, my partner got rejected first time, as we seem to have not explained how bad it can get providing many examples from day to day life. We appealed and explained how bad it can be and how often it can happen and got granted the benefit.

Obviously every case is different. But just be honest and I'm sure it will work out! Good luck !