Goes into "sleep" mode when not on flat surface nor charging

My problem is with the screen going black and the trackpad/keyboard not working. Typically this occurs when the laptop is not on a flat surface (e.g. on my lap) and when it is not connected to a charger. The % battery life is usually between 20-80 percent I'd say when it happens (I don't think that is related. I provide this bit of information in anticipation of that question). The trackpad goes out too. I give it a gentle shake and it comes back to normal. If I don't put it on a flat surface, it sometimes goes in and out every ~five minutes. Anyone know what the issue could be? Details.