It's not the teaching itself that I find tiring, or being forced to rethink stuff that I learned several years ago - indeed, I find both of those aspects quite rewarding. However, I do find actually standing up in front of a load of people and talking for an hour both physically and mentally tiring, and I usually need to have a bit of a rest before I'm able to focus on mathematics again.

Thanks for this. I often find myself in the first situation - after I've spent an hour teaching first-year undergraduates about analysis or linear algebra, I'm too tired to focus on any research. Maybe the solution is to go somewhere quiet and read a non-mathematical book or pop home for half an hour to do some piano practice (conveniently, I live about five minutes' cycle ride from campus).

A similar "access grid" network comprises the Universities of Bath, Bristol, Oxford, Warwick and Imperial College London. The main site (which includes links to archived course material) can be found at tcc.maths.ox.ac.uk.