How to explain that Daddy is unwell

Hi all,

My partner is diagnosed with Bipolar I, ADHD, and panic disorder. We've also had some doctors mention schizophrenia but have not had that documented officially.

Id love to know what/how do you explain to your young kids about their parents behaviours/state?

My partner for example when manic leaves the house for anywhere between 24hours to a week. And then when on a low spends 3 days to a week in bed (his condition is not managed well/he is not stable atm)

Our oldest is 6 and she is now asking questions about her dads behaviour and time away. He has always told her he is going away to work but I feel she knows it’s something more from his behaviour before he leaves and again when he returns.

I was thinking of now trying to explain to her in the best way I could to a 6 year old, that daddy’s brain is sick.

Anyone have any tips or experience with a similar situation?

Thanks