I suffer from CONSTANT anxiety and know exactly how you feel. It makes one feel really helpless, especially the depressive moods and the demotivation. The demotivation is a real killer, because it makes you feel like a "lazy layabout", which is really not true. I can truely sympathise with your situation.
Have you concidered going for counceling? Even if it is normal day to day stress that brings on your anxiety, it won't hurt to talk to a doctor...even just your GP. They can prescribe you pills to get you over the "worste" of your stress/anxiety to allow your body and mind some breathing room to recover from all the stress that has most probably built up over time.
Hang in there...you are not alone
Seraph