All you have to do is go to the “App Settings” page and tap on “Pause My Account”.
If you pause your account, you'll completely disappear from the application. The people you Crushed with won't see you and won't be able to talk to you anymore and your profile won’t be displayed in other users’ Timelines.
If you want, you can be invisible on happn for 8 hours. Your position will no longer be updated, no one will cross paths with you and you won't cross paths with new people.
Careful, if you are Premium, pausing your account won’t cancel your subscription!