If you can’t think of something pleasant, stop thinking. Attempt to quiet the mind through the practice of meditation. And if that fails, resort to extreme fatigue, shutting down the ability to think. Stay awake until exhaustion makes it impossible. When beaten down by tiredness, there is no choice but surrender.
Don’t attempt to shift from negativity right into positivity. It’ll grind the gears. Being overly positive during a negative time is like trying to run on a broken leg. “I can do this! Ugh ow ahh!” Nope not gonna work. Just rest, don’t aggravate the injury.
Get to neutral first. Stop, then go. Think of a wound, constant contact keeps it open, it can’t heal. Leave it alone and it’ll heal on its own. In this way stop the thoughts, stop engaging them. There’s no need to be positive at this point, just get to neutral.
Give it a little time then try some baby steps. Think comforting thoughts, visualize desirable outcomes, see how it feels. Always get back to neutral if things start to go negative. But don’t remain forever in neutral, always intend to get up and move forward.