Calming someone who is having a bad trip.
Talk to the person. Ask them simple questions like what their name is, where they live, how is work or school. Remind them that everything they are feeling is caused from a drug and it WILL wear off. Tell them that everything is okay with you, and that the real world is fine. Ask them if they want to be held or if they want space. If they don't want to talk, don't make them talk. Just remain calm, everything is alright.
Calming someone who is having a bad trip.
the best thing to do... like liquid said, talk to them... people freak out, because they are overwhelemed by the activity in their head... talk to them, chill with them... the worst thing when trippin is being all alone... try to help the event, not change it... dont forget this person is not responsible right now for anything... even themself