Pushing sternum as hard as she can and looking like she's going to pass out

This is a weird one and kind of hard to explain, so I'll start with the video link: https://ift.tt/33EIBmV anyone seen anything like this before?My 18 month old daughter constantly pushes her sternum as hard as she can against the tray on her high chair. She also leans her head back really far and the longer she does it the more it looks like she is going to pass out.She's been doing this for a couple of months now, but until recently we thought she was just unsuccessfully trying to take a dump (it looked exactly like that). The head leaning and looking like she's going to pass out is fairly new. It's also only her sternum that she's pushing. At first we figured she may also be pushing below the belt, but that's not the case.A few weeks ago she helped out in a class on baby massage taught by my wife's friend, and the the friend commented on how tense her neck muscles are. via /r/Parenting https://ift.tt/3ae07B5