Its not uncommon to feel depression at this point, we are all capable of understanding that.
What's more significant from your description of "dread" or tachycardia, or waking up and just staring at the ceiling (ill assume it means not able to fall back asleep or up because of a little anxiety/something on your mind) and always "for no reason at all" is a very typical presentation of generalized anxiety disorder, or you're experiencing panic attacks.
I am by no means saying this as "I study medicine therefore I think its X" but I have dealt with panic attacks since the age of 8 and those things sound pretty typical to me. A feeling of dread, for apparently no reason at all.
You have to identify your trigger. It could be anything, a thought pattern, an unconscious feeling of being trapped, not in control of your life, or having and increased amount of responsibility to not sure you can handling.
I've had anxiety attacks when I get home, despite having a really good day, and kicking butt, but then the slowing down too quickly from the excitement or from being around others, to immediately being alone, sometimes triggers that feeling.
Or coming home, feeling like my whole day was just work, a feeling like I missed something, just a weird/hard to explain type of panic.
When it keeps happening, try to identify the trigger, if its always when you get home after getting off work, that can be pretty telling. Do you think you forgot something? Did you enjoy it too much? Did you hate it so much you dont want to go back? Lots of stuff to think about.