Best advise: "Don't google". My grand daughter born 8 weeks ago, showed too much weakness in the upper body. She would not move as other babies would. So they tried intensive physiotherapy and exercise and it seems to work out well. Anyway in the first dialogue between the doctor and the mother, he said that it could be a number of things, but most of the time physiotherapy proves to be adequate. And whatever you do, don't google. There is little doubt that googling will find you the worst possible diagnosis for any symptom and humans are known to be a bit hypochondriac. However diagnosis is a complex process and we tend to fall for confirmation bias so that we are pretty convinced that we have the worst possible illness, where the odds are that we don't So I think the best possible advise is "don't google", leave it to the doc.