Chances are (without me knowing where you live), you either were a victim of salt air (living close to the sea) or moisture (humidity) absorbed in your mattress. The brass has a tendency to turn especially when copper (jacketed or JHP) bullets are used.
I've found that using a sock sprayed with WD40, CRC, silicone or other lubricant will help keep most pistols free from corrosion in storage. An added protection would be to put the sock/weapon in a plastic zip lock and in your chest-of-drawers. I believe the wood and clothes in the chest-of-drawers may have absorbed any moisture before it got to your holster.
As far as not being able to hit the target...unless your barrel is warped or your adjustable sights were off.....it's a point and click device bro

Rapidly snapping
off rounds leads for a shooter who is not proficient (3 months no range time) to "pull" the weapon to the side upon firing.
Check your grip, try using the ball of your finger, the first digit only on the trigger...inhale, exhale and as you reach max exhalation, squeeze the trigger gently until discharge...you should see an improvement in your marksmanship.
Try shooting "front sight only", both eyes open, combat stance, placing the front sight on the center mass of your target. The front sight seen clearly, the target a bit out of focus...this should put you "on the paper".
Drill yourself on single shot, double and triple tap sequences and practice your breathing technique...fire on exhalation and build up to rapid fire sequences. Marksmanship takes technique and practice.
being effective in a defensive situation requires practicing from different positions, angles and locations. If you're defending your home, "walk the walls" entering each room as you would to clear it in the event of an intruder...practice clearing from standing and crouching positions to get a visual idea of how your home looks at different heights...a table when your standing is not an obstacle, however, when crouched, on a knee or lying prone, it blocks your sight path....hope this helps.