As you probably know, Orapred is a corticosteroid and is prescribed to treat asthma, obstructive pulmonary disease, and other inflammatory conditions. Often, when corticosteroids are prescribed to children, they experience increased energy and intensity, not the sort of calming you noticed in your son. I am not familiar with such a result, and it would likely be unwise for a child (or adult) to remain on corticosteroids for a great length of time. But, let your physician know of your observations. There may be an artifact of the drug's influence on children with Down's with which I'm not familiar.
ok. I am certainly not a doctor. But could that medication have contributed to treating a sleep-disorder? I am specifically thinking of Children's Sleep Apnea/Obstructive Breathing. Allergies, sinus infections, large tonisil and adenoids can all contribute to reduced oxygen/breathing at night for children. Resulting in an overall sleep-deprivation (which in children can manifest as poor focus, excitablility/hyperactivity, poor impulse control, etc. basically ADHD-like) and other events like night-terrors. Often medications that are stimulating or treat the initial problem, even temporarily (eg, allergies), lead to changes in children's behaviour for the duration of the medication. Perhaps, because you mention the sleep difficulties, it would be worth discussing with his pediatrician. Also do a search for sandman's website and read in the children's sleep forum (especially monica's posts; her children had this and she posted quite a bit of information).