I've experienced everything you're experiencing at the moment and more, sometimes on a daily basis. Multitasking for me tends to lead to increased anxiety and confusion, which leads to excessive worry, which leads to more anxiety, etc... I've been having nightmares for about the past two weeks. When my anxiety gets bad I tend to become unhappy as well. And I forget things about two minutes later, usually because my mind is in a constant state of worry. I've had all kinds of tests done, including an mri of my brain and blood work; nothing ever shows up.