Losing energy during workouts

Lately I've been losing energy during my workouts. I normally workout for say 40 mins, and towards the end I feel a significant loss in energy, and it significantly affects my determination/motivation - ie "lemme just lift so I can get it over with".
This is a terrible attitude to have, and I'm sure if I had more energy I'd be more motivated.

Anyway, what could causing this? I can't see anything wrong with my diet, I always get a good mixture of p/c/f.
In fact, I have a feeling it has to do with a lack of oxygen, because my head of starts feeling a bit hazy. Why could this be? Could secondary smoking be a possible reason? Cos lots of my firends smoke.
Should I start some cardio to increase my lung capacity?
Also would eating something like a banana before/during a workout help (something to do with potassium and oxygen absorbtion)?
I've tried taking energy drinks during a workout (Lucozade, Gatorade), but they didn't help all that much. I was still feeling the same towards the end, which is why I think it's not diet-related (of course I may be wrong).

Anyway, I'm not too sure what else to think/do - that's why I'm asking here to see what advice you guys have. Thanks!

Lot's of factors....and secondary smoke sucks,,,

Things that help

1) Watch Pumping Iron
2) Get a training partner
3) Better music
4) Stimulants (careful) Caffeine, green tea, guarana, thermos
5) New Gym
6) The opposite sex, or?
7) lot's of sex
8) etc

DP

Originally posted by kanun
Also would eating something like a banana before/during a workout help (something to do with potassium and oxygen absorbtion)?

Click to expand...

Well, as DP said it could be many factors, however the banana is a great choice as part of your post work-out meal. Bananas are high in glucose (which is the prefered carb) to restore depleted glycogen stores.

Instead of during a workout try before. Maybe 30 minutes before chug a redbull.

And get more sleep :]

Yeah I was going to say look at the amount of sleep you're getting first and foremost.

I notice a huge difference on days where I didn't get to bed at a decent time and days where I got enough sleep....

Sleep is definitely important, but the diet should always be looked at first IMO.

Ingesting a sugar loaded drink, like Red Bull, to get energy before a work-out is not really the best solution.

Food = energy <<< so examine the fuel!!!

Thanks guys.
About sleep: how can you be sure how much is enough? Is feeling awake when you wake up a good enough indicator that you've slept enough?
On days when I have to wake up at a certain time, I try to sleep for 8 hrs but I'm always sleepy when I wake up (perhaps because of my rude awakening).
On weekends I jut let myself wake up naturally, but sometimes, although I feel awake when I wake up, I wouldn't have slept that much - say just over 8 hrs.
Does this mean anything, or should I just sleep as long as my body wants?

Have you changed your workout recently, or have you taken any time off from lifting, like a week off out of the blue. Changing routine helps especially if you've been going pretty heavy with the weights for a while.