Re: Ukemi and Dizziness
189 tall and 69 kg suggests you are quite thin, like a lightweight rowing athlete (must average less than 70 kg in a crew and are frequently around 189 tall). When they're "down" in weight, they get dizzy standing up. I'm not advocating that as a healthy lifestyle, although rowing is one of the better general fitness sports.
If you're that tall and light, what is the body composition - are you athletic, well fed and getting a lot of sleep, or are you a "couch potato," poorly nourished, and sleeping less than 4 hours/night? There may or may not be links to your depression, sports background, nutrition, rest, etc., but it may be that ukemi is causing your balance organs to have new sensations, and you just need to work gradually into aikido - practice ukemi at home a little at a time, and see if you gradually overcome the dizziness you mention. Back pain and stomach pain - is this sore muscles that someone experiences when they start new exercise regime or (respectively) a back injury and gas/nausea or related?
Questions, questions - sorry, not much help..