If you want to talk about karmic obstructions it becomes too wide a field. But we can help these conditions using concrete methods. You can relax your body doing exercises beforehand ─ head and body exercises. And when you sit, make sure your back is straight and your chin tucked in. It's fine if your back is slightly bent, but only if you aren't sleepy. As soon as you feel sleep coming on, straighten your back. Do some deep breathing. If deep breathing alone does not work, you can couple it with hunching your shoulders and then relaxing them. You can also stare in front of you with wide-opened eyes, until they well with tears. All these techniques help to clear a drowsy mind. If you are always sleepy, then sit for ten minutes and then get up and exercise. Even ten minutes of sitting is useful. After exercising, you can try to sit again.

STUDENT:

You have told us not to sit at noon and midnight. What if it is the only time you can sit? Also, in The Three Pillars of Zen, Kapleau Roshi says noon and midnight are good times and one should avoid dawn and dusk. Time of day is time of day, so why are there differences? Is it individual preference, or is there a greater importance?

SHIH-FU:

Meditating occasionally at noon and midnight shouldn't be a problem, but it's best not to make it a regular habit. Ten to thirty minutes into those periods is still okay.

What Kapleau Roshi says might be true for him. I don't know if it is his personal preference or if it is something more. Normally, though, at midnight you should be asleep or at least tired and resting, especially if you have been working all day. Avoiding noon and midnight comes from the philosophy of Chinese medicine. It is not my personal opinion.