Take someone with you by all means.
Neither you not the note-taker can see what the assessor is typing whilst the assessment is taking place, that's why it's important to ask for a copy of their report, although considering how fast my relative's assessor was typing and how much she typed, Id guess that the final report is just a precis of the typing done at the assessment, but it's that final assessor's report which DWP seem to consider as Absolute Truth, despite any contrary medical evidence you've already submitted.
This is the crux of the problem. When the assessor's report is different to your own medical evidence and contradicts it, DWP insist the assessor is right. They do that at MR, that's why so many people go to Tribunal, because at Tribunal, the panel look at all of the medical evidence you have submitted, not just the assessor's report.
I think one of the best bits of advice upthread is when you're answering the assessor's questions, don't try and downplay your condition, describe it as it really is. Don't answer questions with Yes, but... if it's something you have difficulty with most of the time, because they only register the 'Yes'
Practise answering with No. We are all taught to be polite and not to discuss details of our health issues with anyone so it is unusual to be forthright about personal things.
You may get an assessor who knows about your condition(s) and who does a fair assessment for you. You just have to be prepared, just in case you don't. 