Yes, it is true that if you are not well-hydrated before exercise, you will get dehydrated leading to
fatigue and sometimes
fever too.
Are you doing intense workouts? Your body might be finding it difficult to adapt to the level of activity. If you have been inactive for a long period, then you must begin slowly otherwise you will get fatigued. You have not mentioned your age and whether you are exercising in a gym. Begin with low intensity exercises for short duration rather than starting with moderate to high intensity workouts. It will be best if you gradually increase your physical activity.
You must have worked out for a longer duration than your body can handle. If you are exercising in a gym, then you must begin under the supervision of a gym instructor. Ill-considered exercise can cause fever and fatigue as it puts your body under
stress.
So, remember:
1. Begin slowly and build up gradually.
2. Be regular and avoid high intensity work outs till your body adapts to increased activity levels.
3. Short bursts of intense activity done irregularly can do more harm than good.
4. Drink plenty of water before and after exercise to keep yourself well-hydrated.
5. Do not work out when you are ill or tired. Take a break and rest well.
Hope this will guide you better in taking up an exercise programme.