Danger in Aikido
I don't think Aikido will pose any problem for you.
Depending on the style of karate you practiced, you will have to resist punching and kicking, accept manipulations as defense when you open yourself/move your body, and don't drag your feet!
Aikido was modified by O'Sensei, Morehei Ueshiba to leave out killing techniques, but allow the full motion of movements found in Jujitsu, judo, and sword arts without causing undue injury. The really neat thing is ... all the techniques found in our softened style are completly safe.
Sometimes I think that there are more injuries in public schools and at home than ever happen in all the martial art classes in the world?
When I switched to Aikido, I had a lot of trouble learning to move my entire body or one side of my body in unison, but with time it happens. Then it really starts to become fun!
Listen to warnings about dragging feet and little hints, most sensei's only say advice twice, then it is up to you to learn?
But, all in all ... sooner or later ... everything you learned in karate will find it's way into Aikido practice, don't be surprise to find old techniques come back like an old friend?
(Aikido allows laughing/smiling too!)