I've given many times over the years. Coming up to 50th shortly. It used to be a pain when they made you lie for 5 mins afterwards, and then have a hot drink. But gradually they're getting more relaxed. First you could have a cold drink instead of the hot one - less time to wait. And then last time I gave, they relaxed the five min lie, and said I could get up an leave the bed as soon as I wanted.
Only once did I feel faint, and that was on the way home afterwards. I'd cycled that time. But since then, I drive or walk, with no problems whatever.