Yes, if your doctor says "no ALS," you can trust him. They typically don't give guarantees so when they do, you can be pretty sure! I was never told that by my doctor, he used words like "unlikely" and "probably don't." As others have mentioned, ALS at 25 is extremely rare, very few cases occur before 30. There are some people who have contracted the disease in their early 30's but even that is rare considering the average age of onset is 55 or 56! I'd be willing to bet that you have BFS or something much more benign, I'd also be willing to bet that your symptoms will wax and wane with stress and other factors. Try to exercise, eat a well balanced diet, take some extra vitamins and limit stress.