You should see an emergency doctor or go to the nearest emergency room
immediately if you were unconscious or are hurt. The doctors there are bound to
professional secrecy. Tell them that you suspect having been raped or abused under date rape drugs.
Ask for the injuries to be documented, for pap smears to be taken and for blood and urine to be tested for the substances used as date rape drugs. Be aware, however, that this is not a standard insurance benefit and will be done (or not) at your doctor's discretion.
Not all medical labs can test for the substances in question; the forensic medicine institute in charge should come in then. In Berlin this is the Charité Institute for Forensic Medicine ( Rechtsmedizin der Charité).
Again, it is important to not wash or shower before a medical exam and gathering of evidence.