Stress can have an impact, but since you release cortisol when lifting anyway I'd doubt that.
You could, if you're knackered, try mixing up a pre-workout, which contains caffeine and wash it down with a banana. That's one of the few times I use a pre-workout, just to help get that focus especially if I'm pushing myself and am feeling run down.
Just for interest:
This is how some of your hormones respond to a work out. Thyroxine (a thyroid hormone) also known as T4, increases the calories you burn when exercising. The response of this is by increasing your body's metabolic rate of many the cells in your body. So as you can imagine this is useful for utilising excess glucose/sugar in your body as well as burning fat for energy. The downside is that it does not discriminate and will convert amino acids for energy - i.e. it can be catabolic.
If you are in this state for an extended period of time (for example length cardio sessions), and lack enough sugar/glycogen to use as energy, you might start lose muscle - if you're not fuelled this will have a more profound effect on energy levels as your body switches energy sources. The less lean muscle you have the lower/slower your metabolism will behave.
During a work out epinephrine also increases your metabolism quickly (think fight or flight) allowing sudden increases in activity levels. It generally scavenges for fat and sugar for energy, however as usual it will also target amino acids (i.e. muscle) if there isn't enough or a sufficient store of sugar or fat in your body. This hormone production is proportional to both exercise intensity as well as how long you're training for. As above the longer you maintain intense training, the bigger the effect and metabolic boost you'll get from it. Epinephrine directly contributes to increasing your metabolic rate after heavy weight lifting.
Lastly, insulin. As we know it regulates your blood/sugar levels. High levels of insulin can cause a sudden decrease in blood sugar since it works by metabolising available sugar. Although this is not always a negative (since high levels of insulin also help shuttle sugar into muscle tissur post workout). However, after a tough workout, your blood/sugar will crash since your insulin levels will be high. Hence why you can feel dizzy and light headed - there is a link to blood pressure, too but that goes beyond my immediate knowledge. You can of course take advantage of this heightened state of insulin to take nutrition or something to give you a boost of energy. Typically I'd recommend an electrolyte based drink, however, a lot of people like to take shakes.
So these hormones can have a compounding effect on you if you're not in the "right" state.
There are of course a lot of other metabolic pathways and hormonal responses which can affect your performance.
That's my last minute pre workout tactic too! Not ideal but better than nowt.
