4 months old fell from bed

My son just turned 4 months and he fell from bed this morning. We're using a queen sized bed... it was awhile when I turn away and I don't know how fast he roll over. He's cried for like 1 minute before I carried him and hugs him tightly. I straight away make some milk for him and fed him. He's drinking well. He smiled when I talk to him. So far nothing serious but a bruised on his front head since he fell.. his face on the floor. I am so scared. Sorry for my English... I can't write properly as I'm shivering. He's my only son