Try 'Olbas Oil' available from the chemist. Just like Menthol (in fact it contains it, along with a load of other oils), it doesn't say to use it like this, but I drop it in hot water and inhale it as described above. Seems to work quite well. Also good for a sniff if you need to unblock suddenly.
Sudafed or Pseudoephadrine (spelling?) should not make you drowsy, in fact the opposite (don't take at night!), but it does "impare psychomotor coordination" which is why it is not liked for flight crew! (comes from a presentation given by an RAF doctor and relies on my memory, which may well be wrong.)