Not that I've experienced it myself but I found this on a website and it seems quite similar to what my friends have described.
Braxton Hicks contractions:
Are infrequent, and usually happen no more than once or twice an hour, a few times a day.
Often stop if you change activity. So walk about if you've been sitting, and sit down if you've been on your feet for a while.
Are usually irregular, or if they are regular, only stay that way for a short spell.
Don't last long, usually less than a minute.
Continue to be unpredictable and non-rhythmic.
Don't increase in intensity.
Compared with Braxton Hicks, labour contractions are:
noticeably, and increasingly, longer
more regular
more frequent
more painful
increase in frequency and intensity
Prelabour is when Braxton Hicks contractions may come more rhythmically, perhaps every 10 minutes to 20 minutes in late pregnancy.
Prelabour can be hard to tell apart from early labour, particularly if the tightening of your uterus feels uncomfortable. During prelabour your cervix won't have started to open yet. Your midwife will be able to tell by carrying out a vaginal examination.
If you have any doubt I would call and check with your midwife. I'm sure she would rather you called and everything be ok than not and have something happen.
Hopefully someone with more experience will be along with more advice. I hope all's ok. X x