Have you thought about...
In London, the Iyengar Institute in Maida Vale is amazing. Hot / Bikram yoga is also pretty accessible.
Are you drinking at least eight glasses of water a day? Are you getting enough vitamin C and essential fatty acids in your diet? Recommended reading on how diet affects your health includes "Beat Stress & Fatigue", "Optimum Nutrition for the Mind" and "New Optimum Nutrition Bible", all by Patrick Holford.
Meditation can reduce stress and anxiety. Acem Meditation is a non-relgious form of meditation developed in Norway by doctors and psychologists to aid relaxation, energy, health and personal growth. Courses take place around the UK.
Studying something fun
Central St Martins College of Art and Design - evening, weekend and holiday courses
City Lit - huge range of short courses covering a large range of subjects
The Open University - very slick and professional and offers a large choice of courses
Hot Courses - lots of choice here
Leiths - unwind after work at this famous school
Books for cooks - workshops at a cute Notting Hill venue
Go ape - swing from trees to unwind!