Recently an article of mine regarding standing vs. supine HRV measurement was posted here. The article includes;

• A brief discussion of autonomic control of heart rate during supine rest and in response to orthostasis (standing)
• A summary of some research pertaining to standing HRV measurements
• A presentation of data I collected over a 2 week period where I measure and analyze both my standing and supine HRV scores in response to training load.

Check it out here.