How to talk to my husband?

I struggle with several mental illnesses (bpd, depression, anxiety, etc) and partly because of that it is REALLY hard for me to express my feelings to my husband.
I can be really upset about something (usually several things) and I can sit there and think of them all in my head and it makes perfect sense but as soon as he asks me why I'm upset it's gone! And I'll I can do is shrug. He gets angry and walks away and I end up even more upset with myself and him for not being understanding...
It doesn't help that when I do manage to tell him something he shoots it down or gets defensive... So then I don't even want to try.
Does anyone have any suggestions?? How should I deal with this? Thank you!