i 've been there ,i once drove all the way to class ,just to decide it wasnt feeling right .then went home.
i think its the routines of everyday life,and getting caught up in it.
alot of times its hard to settle the mind from the faster paced city life.
try to warm up for training at home before class ,meditate to calm the mind.
i also like to skateboard, and my friends and i watch skate videos just to get "amped" and in the mood for skateing.
so it might help to read about Osensei, or whatever it is that keeps you excited and interested about aikido.