Something shaking the bed? Ghost?

My girlfriend was sleeping in our basement after she had lasik surgery and she said she was woken to something shaking the bed. Her 2 year old son and i were the only other ones in the house and we were both up stairs. Also at times her son will be sitting there just staring at nothing and all of a sudden he will start talking to someone. Usually he just waves and says "bye-bye" to nothing. What should we do?