Hi Lily1 , I have had exactly the same fear . Mine started nearly 3 years ago with the ALS fear .
I have feared many diseases over the years , mainly cancer , until I discovered ALS after my knee started to twitch and this fear hasn’t gone away .
I too have studied my tongue constantly to a point I have made my tongue and the inside of my mouth sore . And yes on times it twitches and so does the rest of my body .
I honestly think that anxiety can give you the symptoms of the disease you fear , we are so in tune with our bodies that we feel every little thing , that most people would overlook .
ALS is a terrible disease and a frightening one , but you are not alone . I am really trying to stop checking myself , distraction is my best cure , I hope this helps .