My DS had silent reflux and it took untill he was about 3 months old to get diagnosed. He was the opposite of your DS, he slept well at night usually from abou 9:30-3 and then again untill about 6ish, but was HORRIFIC during the day, unsettled, restless, easily disturbed. Once he was on Losec he was a different baby, and I got my sanity back for the first time in months.
I am pretty sure that Losec won't do any harm, it just inhibits the production of stomach acid (please someone correct me if I am wrong). It did take a good week or more for us to see real improvement, but once he did improve it was a HUGE improvement. DS is off it now and has been for about 5 months, and he has had no side effects etc from taking it.
My suggestion would be to try it for at least 10 days and see if it makes a difference, if not then you can stop, and no harm done.