Steep waves

I encountered a new kind of problem today: really steep waves. At least that's what it felt like. The waves were pretty big by my standards (I'd say about four foot) and were easy to paddle into. However, as soon as I tried to stand up, my board would just rush off the wave, much faster than I could find my balance. This was new to me, I usually do pretty well on this size of waves.
Any way, the whole thing kept ending up with my board flying away from under me, while I just free fell off the top of the wave, hit the water (which felt more like hitting the asphalt), and then went under while the wave crashed on top of me. If anyone has any advice, I would sure appreciate it.
And while I'm at it: I also have a small follow-up question. I keep reading that I am never allowed to let go of my board (a minimal), that I have to hang on under all circumstances. Today I was trying, but I just couldn't hold on when the wave crashed on top of me. The board would fly off backwards, I got nasty looks from the people behind me, and I now have severely sore arms from clutching to the board. What am I doing wrong?
Any way, the whole thing kept ending up with my board flying away from under me, while I just free fell off the top of the wave, hit the water (which felt more like hitting the asphalt), and then went under while the wave crashed on top of me. If anyone has any advice, I would sure appreciate it.
And while I'm at it: I also have a small follow-up question. I keep reading that I am never allowed to let go of my board (a minimal), that I have to hang on under all circumstances. Today I was trying, but I just couldn't hold on when the wave crashed on top of me. The board would fly off backwards, I got nasty looks from the people behind me, and I now have severely sore arms from clutching to the board. What am I doing wrong?