I have had depression since February and have successfully hid almost every symptom from everyone I know, with two exceptions (my friends who help me with it). I even went to Disneyland with my family recently, and even though half the time I felt like happiness was just straight up a lie humanity tells itself to make itself feel better, and no one ever caught on.
Occasionally a really bad episode of something akin to a panic attack (but not as bad) will happen while I'm around other people, and those I can't hide from anyone. I can only try my best to get over it and hide it again as quickly as possible, at which point I can give some excuse for my behavior. ("It's just nerves," "I didn't sleep well last night," etc.)
Hiding depression, or any mental illness I suppose, is incredibly tiring and incredibly draining. If you aren't in a position where it's just simply necessary (I unfortunately am), I highly suggest not trying to hide it. Take care.