Its perfectly natural for the krausen (what you called head) to fall to the bottom (now called trub). In fact, that's what happens during fermentation. Visible signs of fermentation aren't the best or most accurate ways to know when fermentation is complete. You may not have any airlock activity or other visual signs and your beer is still fermenting happily.
Take gravity readings. When it doesn't drop for a few days to a week you're probably complete. So long as it hits near your target FG.
As for secondary, many brewers do not use a secondary at all, but rather leave the beer in primary for 3-4 weeks total, then bottle. That's what I do and I get clear, delicious beer. If I am dry hopping or adding things like coffee, I'll do that in my keg, or use a secondary for about a week.