Hi, Anonymous —

You said:
Is sleep masturbation still a sin?

If one:

• was asleep, and unconscious, <no, it is not a sin>
• was partially asleep, therefore did not have full consent of the will, it would be a venial sin.

In order for a sin to be a mortal sin, you must have full consent of the will.
If the person does not have full consent of the will, there is no mortal sin.

You said:
Should I still go to Confession?

For sins like these, I would personally recommend going to Confession.

Don't be scrupulous, just mention the sin to the confessor and say:

• You want to may good holy Communions
  and
• Offer the Confession up for others around the world that struggle with this prevalent sin.

Mike