I wouldn't jump to brain tumor right away. Hiding in his box for most of the day when he doesn't normally is a "red flag" that something's not right. He should be checked out by your vet, and maybe his spraying has some medical reason as well.
Blowing in his face for hissing only antagonized him further; most cats hate that. Raising your voice definitely won't calm a cat. I wouldn't use blowing in his face as a disciplinary measure for anything. He was upset his claw was caught. Better would have been a soothing, sympathic voice. "Aw Gizzy, got your claw caught? Here, let mommy help you" while you unhooked his claw, and ignored his hissing, then give him a pat and say "Poor baby". Claws should be clipped every 3 weeks, so this doesn't happen again.
Because Gizzy's been spraying again, and you're upset about it, he may be feeling grumpy anyway. It's sounds like he's starving for attention "shoves his head into your hand" and "screaming at me to pet him". The "pet him a couple of times and then go about my day" aren't enough for Gizzy. Are you withholding affection from him because you're angry at his spraying and now hissing? Maybe he's reacting to feeling neglected? I think you should give him good quality one-on-one time----spend at least a good 15 mins./day just playing with him, with a teaser toy, dragging a cord around for him, throwing toys for him (does he retrieve?), grooming him once a day (if he enjoys it), give him lots of petting, chin and cheek rubs and kisses and "good boys". Right now Gizzy's not a happy camper for whatever reason...yes something's changed.