Izuku doesn't seem like the depressed type, does he? Not with the happy, determined smile he pulls off. Needless to say, no one notices when those smiles start to become fake. That's what Izuku thinks anyways.
Aizawa has other plans
"She can speak rudely, but she also suffers from pain"
"Someone opened up the floodgates and now she's drowning"
"She was drowning, but nobody saw her struggle"