I used to get rebound congestion after using decongestants a lot. But I discovered that it doesn't happen if I don't take decongestants for more than three days. So what I do is I use it at the recommended dose for three days. Then, I take a break. If I don't need them again, great. If I do, I resume the dose after several days. This prevents rebound congestion.
@anamur-- By the way, I heard that decongestant nasal sprays don't cause restlessness and anxiety as much as the oral drugs do. Maybe you should give that a try.
You could also try doing steam inhalation or rinsing your nostrils with salt and hot water. These are great natural ways to treat congestion without side effects.