Are these the same?
You're stoping so low.
You're sinking so low.

Question

Are these the same?
You're stoping so low. 
You're sinking so low.

Answer

"you are stooping so low"  means your behaviour is below the moral level of acceptance,                                          
  (this is a verbal form of  rebuke)

Answer

It must be "stooping", which originally means that you are bending your body forwards and downwards. I guess it means here in this sentence that you are depressed.

Answer

* stooping.

They are similar however stooping is a result of you own doing, mostly in your control. E.g by shouting [back] at a drunk person you're stooping low.
Sinking on the other hand may be a result of other factors surrounding you, usually out of your control and sometimes emotionally. For example stress.

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