@PossiblyAutistic@actuallyautistic There are different assessment methods even within each country, so what I’m about to share may vary in its usefulness! But I think it’s very common to be asked about life events across your past where you think autism and/or ADHD traits played a part. They may ask you about specifics like major transitional periods in your life (moving schools, moving home, teenage years), or it may more likely be a case of you offering up memories of events that you think are appropriate.
A common thing they look for is whether traits are recent or there’s evidence during childhood / longer term. Don’t worry too much if you can’t remember - just tell them that you can’t remember. But anything you can remember can be very useful.
I echo the idea about notes - if only to help you remember key reasons you’re seeking these assessments. Assessors are trained to ask questions that help you to remember relevant events, but it just depends on the assessment format. My autism assessment was extremely comprehensive (3 sessions of 1-1.5 hours each), but my ADHD one felt very brief (1 hour only). Neither are better or worse, but I am glad I prepared for the brief assessment as I wouldn’t have had some key memories of my past ready in my mind otherwise. I can be rubbish at remembering things - even things I have recalled only recently and told myself to remember!!
“Being yourself” is certainly important, but can feel almost impossible in an assessment. They are usually very aware of “masking” and the anxiety most will feel during an assessment - all very natural responses to such a strange process. So being yourself might include being anxious, masking somewhat. It’s all ok, is my point. You could chat with them about the masking, though, for example.
If you have any questions you want to ask the assessor - have them ready, too. There isn’t usually any chance later on after the sessions. It can feel over and done with very quickly, and like a whirlwind. So have a think about what you might want to ask, especially considering all the possible conclusions of the assessment (whether autistic or not, ADHD or not, ‘type’ of ADHD, etc). When I thought about this, one thing I requested was that I wanted to know if they thought I was ‘borderline’ for any of them, no matter which side of the border of assessment criteria I was on. It’s more information than just binary yes/no that might help me later on. (But this comes with the caveat that assessments and their thresholds for a diagnosis for are human-made, and far from perfect!)
Hope this helps. Very happy for you that you have so little time to wait!