Paul Ekman did a study that found that when participants contorted their facial muscles into distinct facial expressions (e.g. disgust), they reported subjective and physiological experiences that matched the distinct facial expressions. His research findings led him to classify six emotions as basic: anger, disgust, fear, happiness, sadness and surprise. 1
So there is a physiological correlate for each of the 6 basic emotions - my theory is that from different stimuli, different intellectual cognitions (such as thoughts, dreams etc.), and one or more of those 6 basic emotions (or possibly other feelings) consciousness arises. It doesn't necessarily have to be right away, it could take hours for neural centers to respond (in that way more complex emotional responses can be formed since they are possibly a build up of a few hours of mental experience).
This way, from a simple emotionally triggered response (not just emotional, but also intellectual stimuli and external stimuli) in the brain complex feelings arise. The answer must be that different chemicals are stored up over time. In that way only a few basic emotions could give rise to a rich conscious emotional and intellectual experience. Emotions trigger thoughts, thoughts are triggered from external stimuli (in any order thoughts, emotions and external stimuli can trigger each other) (which was triggered by such and such stimulus) could trigger this and that feeling over the next few hours.
Humans must develop a way of organizing the three inputs of emotion, external stimuli, and thought (the intellectual input) over time, and the way their mind organizes the data forms their 'consciousness'. - For instance, if you respond to seeing this object this way emotionally and intellectually - then that was how your mind organized your emotional/intellectual response. It is subjective to decide whether or not you were 'aware' of your response - humans respond to things all the time and they aren't necessarily aware of those responses.
So someone emotions could be sending signals to the part of the brain or body that registers those feelings. Your mind (thoughts, etc. - the intellectual part of your brain) could also be sending similar or different signals about emotion (i.e. 'I want to be happy' or 'I don't want to be angry'). As a third input, the person could be getting signals from their external environment telling their emotions to be happy, sad, etc.