MDD is Major Depressive Disorder, aka Clinical Depression. It's a mental illness that affects mood, but it also comes with physical symptoms. Low energy, low motivation, sadness, overeating, undereating, (I do both) inability to concentrate. It's extremely hard to get dressed and go do things when you're suffering with MDD, even things you know need to happen, even things that might make the condition better. MDD is a disease that seeks to preserve itself. It's not just being down.