Most women (70–80 percent) will experience “baby blues” beginning a few days or weeks postpartum. Symptoms can include irritability, mood swings, crying spells, feelings of tension or nervousness, sleep disturbance, feelings of being overwhelmed, loss of appetite, and sadness. Baby blues generally lasts anywhere form a few hours to a few days and is caused by the sudden fluctuation of hormones following birth.
Source: wiktionary