Hi Anna,
The hindrances, such as I mention in the EC book, usually are to be thought of as arising from an automatic reflex to moving forward in your inner work. Since dark always opposes light, there comes into play an opposing force when you set out to advance consciousness. This opposing force could take the form of outer forces, or it could seem like an inner part of yourself. Then, the type of hindrance you encounter appears in the mind – you doubt, you become restless for more, you resent, or you experience opposition/sleepiness in meditation, etc. If you are tired at the end of the day, however, this could easily be the cause of your sleepiness.
What we normally refer to as resistance is not so much from automatic opposing forces, but the natural inclination of the mind to turn away from pain. Negative feelings are painful, and we intuitively want to push them away, but this works against us, creating suppression. This kind of resistance can be somewhat unconscious. We may be unable to contact feelings at times; or unable to see the deeper patterns because the mind creates a barrier. It’s just a matter of staying present with the process, including the resistance or hindrance. If you feel stuck, witness it, don’t fight it. But you can also try to become aware of the unconscious pushing-away tendency of the mind, and put it aside – it’s a matter of finding that inner tension in the mind during meditation and consciously relaxing it. Resistance/hindrance usually has its own timetable, and we have no choice but to relax and allow it to run its course. Relaxing into it allows it to dissipate.
I have always found Chopra to accurately present traditional spiritual principles for the general public; I’m not familiar with Dawkins.