my lo tend to cry during sleep in the afternoon. very hard to wake him up and calm him down. any solution?

Did he play too much before napping like over stimulated? If my kids played too much like laughing too much til cannot catch the breathe or overly fast/hard heart pumping cos too excited or cried too much before sleeping, all these will cause 'nightmare' in their sleep. I will have to keep calling their name to wake them up and they will be fine.