Why is it harder to pass urine when I get up in the night than it is during the day. Is it because I have been lying down? I do struggle with urinating as I get older but it is worse at night.

Yes, posture will play a part and the symptoms you have described will not be uncommon. This is not helped by the fact that many men over the age of 50 experience symptoms of an enlarged prostate.

These usually take the form of a gradual difficulty in passing water as well as needing to go to the toilet more frequently. This increased frequency is more noticeable at night - and the start to urinate in the middle of the night, known as nocturia, is one of the early symptoms that men notice.
 
It will be worth having your prostate checked out by your doctor. If it is felt that you have a condition known as BPH (Benign Prostatic Enlargement) also known as an enlarged prostate, you might wish to consider the use of Saw palmetto herb  - it can be very helpful during the early stages of the condition.