Sometimes, I feel sleepy when I am doing my weight training. Is this natural? It doesn't happen all the time, only sometimes, I feel so tired that I feel like sleeping immediately afterwards.
I know some people who can have a great workout without fueling ahead of time, but I feel similar symptoms to what you describe if I don't have a snack before I work out. A snack of 1/4 cup of cottage cheese about an hour ahead of time is enough to help me get through my weight training. (I am 160 lbs, so you may need to eat more or less.)
If you eat too soon before a workout your body is focusing its resources on digestion, especially if you eat a high carb meal. That may be part of why you feel sleepy. If the food is too high in carbs you'll most likely experience the 'comfort food' or 'food coma feeling' which will make you feel very sleepy.
Another cause of the drowsiness is caused by the lack of a good warm up. Your energy levels aren't only regulated by food consumption. When you're working out it's also important to have enough oxygen and healthy circulation so your body can transport the resources needed to fuel your muscles.
My suggestion has 2 parts. First, carb load the night before. Ie eat a healthy dinner that includes a lot of pasta and/ or rice the night before you workout. That way you have a large amount of readily available energy. Next, eat a light meal of mostly lean protein a couple of hours before you lift. Just enough to maintain your energy and provide some protein during the lifting but not so much that your body needs to invest too much energy into digestion.
At the very least warm up properly before lifting. Nothing extreme just a light jog to raise your heart rate and get the blood flowing.