Re: Pretty disappointed in myself, looking to fix that.
I'll support that - aikido can be a good workout if you try hard. It just requires three things: 1. good falling technique, 2. a willing and dedicated partner who also wants to work hard, 3. focus.
If you learn your techniques enough that you can perform them somewhat fluidly, then you can focus and really drill through entire katas in a short period of time, which will wear you out.
My old partner and I used to do this for several weeks in prepping for belt tests, just focus - bite down - and spend every second in the class running through entire katas; only pausing when we noticed something we needed to work on.
However, it will take a little time before you know any katas that well.