This can be pulled muscle; though a pulled usually gets better on lying down and aggravates on standing or sitting and doing some work (especially with the back movements). A degenerative disc disease is more likely to cause pain during lying. Though this too is self limiting and gets better usually in a week or 10 days. So you may wait for this much duration, especially since he is feeling better.
Following measures would be helpful;
1) Back care in the activities of daily living, which is an integral component of the treatment of back problems. Back education is one of the most important thing which teaches the basic body mechanics, like correct posture for standing, standing at a desk or drawing board, sitting, brushing teeth, washing the face, pushing and pulling a weight, lifting a weight, getting in and out of bed, sleeping, getting into and sitting in a car. The training for these routine activity helps in preventing the spasm of the muscles. One needs to consult an occupational therapist or physical therapist which can educate about the proper and improper behaviors when back is painful in case they have to sit, bend forward, lie down, walk, cough, or sneeze. Following more need to be done:
a) Avoid activities which increases the pain.
b) Rest intermittently
c) Avoid bending at 90 degrees
d) Pushing and pulling should be avoided till pain subsides
f) Avoid prolonged sitting and standing
g) Avoid sitting or sleeping on floor
2) Anti-inflammatory analgesics like ibuprofen, other analgesics and muscle relaxants
3) Local analgesic gels or sprays / ointment
4) Hot fomentation
5) Electrotherapy like trans cutaneous electrical nerve stimulation: done by physical therapist. Other thing are ice packs, heating pads, electrical stimulation, phonophoresis, iontophoresis, relaxation, and biofeedback.
6) Good supervised physiotherapy: The exercises consist of abdominal bracing, modified sit-ups, double-knee-to-chest or low back stretches, seat lifts, mountain and sag exercises, knee-to-elbow exercises, hamstring stretches, extension exercises, and extension flexibility exercises. Swimming exercises (pool exercises) are best for back pain. Initial stretching and later strengthening exercises are taught.
7) Lumbosacral corset or support or brace
8) If obese or over weight, reduce weight for long term benefit.
You can start the following exercises;
1) Straight leg raising: Lie on the bed with your back and remain in a relaxed position. Slowly raise one of your legs upward and keep it as straight as possible. Count up to ten, and slowly bring down the leg. Do the same with the other leg. Repeat this exercise ten times.
2) Curl ups; lie on the back with knees bent, fold arms across the chest, tilt the pelvis to flatten the back, and curl-up lifting the head and shoulders from the bed / couch. Hold for ten seconds, then slowly lower to starting position. As strength builds, aim to complete one sets of ten curls. The exercise should be done twice a day (both the sets).
This is a slide show for the exercises (he can pick up your own set, which suits him);
It is privilege assisting you.