I am also suffering from loss of focus with too much multitasking. Tired easily and like not completing anything well.
Please, please, please, make sure you read the next two articles, I have put lots of practical advice in them to help you combat this. It's all well and good knowing we should single task, so I will show you how to train your mind in that area.
Thanks for your comments :-)
Cool, will give feedback on your post too @cryptogee!