Having your manager restrict your internet access or a having a break are good ideas, I would say. Don't do what I did in my last job! I tried to hide it, hoping it would just sort itself out. When my lack of productivity got noticed, they checked my internet records and the truth came out, and I was disciplined for misuse of company assets, eventually losing the job.
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When you are fighting an invisible monster, first throw a bucket of paint over it.