It is very normal. Just like anger, grief and sadness, etc. But when it becomes an unhealthy amount, where it's interfering with daily tasks and performance, it's best to try and get in with a therapist as soon as it's an option, because there is hope. No matter how debilitating a sickness may be, or depression episode, stress, anything. No matter what, you are so important, and there is hope. It matters on how you take that and perceive what's going on around you.
At least for me, I've been scared to come out of my "little rock" I've been living under for quite some time now. Repeat hospitalizations,, day patients, 911 calls, therapists, bullying, depression, anxiety, BPD, etc. I am scared because I don't want to leave this familiar place. I am afraid to 'be happy'. I've loved the idea of it; always. But when I try, that depression grabs me right back down. Until and as soon as I can figure out a way to get past that, as soon as depression is trying to sneak up on me, the better a chance I have at making a full recovery, or at least succeeding in my path to true happiness. It's a familiar world, but I have to learn to try to enter new worlds, and be less shy. I've learned a lot from being a listener on here. Giving advice I hardly tried giving myself; because I felt worthless, pathetic, and more.
And for you, or those seeking help, that is a great thing. As soon as you spot the first sign of something, try to advocate or get yourself some help. No one should ever feel like they don't want to get better. It's mostly about attitude, perseverance, support, and hope.
Stay strong you all.