Vacuum hose off ?
Vacuum hose would not cause slipping,low fluid,stopped up transmission filter maybe.
Not likely, if that were the case it would shift high and hard not slip and besides I don't think these have any vacuum lines to them, everything is electronic, so if it is slipping then it is most likely something internal, could be a solenoid or a line pressure problem, best to have it check by a good tranny shop before it completely goes away. HTH
Looking for a Used Civic in your area?
CarGurus has 3,811 nationwide Civic listings starting at $750.
Search Honda Civic Questions
Honda Civic Experts