Here are a few "tactics" I employ when I need to just dive in and dejunk.
1. "27 Things" -- I think the Fly Lady calls it a 27 Things Fling Boogie, but the idea is to get rid of 27 things in one fell swoop. Start with obvious trash. Every handful or big item is 1 thing. After that, grab a bag or box and start putting more things in it till you get to 27. Then give yourself permission to Stop. I would guess you could find 27 pieces of fabric or zippers, a UFO you don't like, notions never used, etc.
2. The Mt Vernon method. The name comes from the housekeepers at Mt Vernon. They clean by starting at the door of a room and work counterclockwise, one section at a time (not zigzagging across the room , not leaving the room) till it's done, then move on. You can easily see your progress if you concentrate in dejunking one area before moving on.
3. Set a timer. My most often used method. 15 minutes is my norm. I work uninterrupted for 15 minutes. Then, if I still have motivation, I set another 15 minute timer. I'm usually good for 1.5 hours till I'm burnt out from decision making, but if I set a timer for 90 minutes, I would feel overwhelmed. Bite sized chunks of time work better for me
mentally.
4. Before and After Photos. I sometimes do this when I'm overwhelmed. I take photos of the whole room, then photos of each section I want to tackle. Set the timer for 15 minutes, work fast, taka a photo. It's amazing what we can do when we race the clock and then see progress via a photo.