How about trying lots of short bursts, rather than spending too long revising one subject? Set yourself self a single, achievable goal per 10- or 15-minute session. For example, learn the make-up of the electromagnetic spectrum, or a single circle theorem, or something like that.
Then take a quick break and move in to the next topic.
At the end of the day, do a quick recap to re-enforce what you've learned. Do another recap in a fees days time, to help solidify the knowledge you've gained.
(I've no idea if this would work for you, but it's worth a try.)